Intra-Prediction Using a Cross-Component Linear Model in Video Coding

ABSTRACT

A video coding mechanism is disclosed. The mechanism includes receiving a video signal partitioned into a chroma block and a first neighboring luma block. The mechanism also includes encoding prediction information for chroma samples of the chroma block into a bitstream. The prediction information for the chroma samples is determined via intra-prediction based on down-sampled neighboring luma samples. The down-sampled neighboring luma samples are generated from a single row of luma samples from the first neighboring luma block. A bitstream including the prediction information for the chroma samples is transmitted to support decoding and display of the chroma samples.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of International ApplicationNo. PCT/US2019/041526, filed Jul. 12, 2019 by Xiang Ma, et. al., andtitled “Intra-Prediction Using A Cross-Component Linear Model In VideoCoding,” which claims the benefit of U.S. Provisional Patent ApplicationNo. 62/697,268, filed Jul. 12, 2018 by Xiang Ma, et. al., and titled“Intra Prediction Using Cross-Component Linear Model,” which are herebyincorporated by reference.

TECHNICAL FIELD

The present disclosure is generally related to video coding, and isspecifically related to using luma samples to predict chroma samples viaintra-prediction as part of a video coding mechanism.

BACKGROUND

The amount of video data needed to depict even a relatively short videocan be substantial, which may result in difficulties when the data is tobe streamed or otherwise communicated across a communications networkwith limited bandwidth capacity. Thus, video data is generallycompressed before being communicated across modern daytelecommunications networks. The size of a video could also be an issuewhen the video is stored on a storage device because memory resourcesmay be limited. Video compression devices often use software and/orhardware at the source to code the video data prior to transmission orstorage, thereby decreasing the quantity of data needed to representdigital video images. The compressed data is then received at thedestination by a video decompression device that decodes the video data.With limited network resources and ever increasing demands of highervideo quality, improved compression and decompression techniques thatimprove compression ratio with little to no sacrifice in image qualityare desirable.

SUMMARY

In an embodiment, the disclosure includes a method for cross-componentprediction of a block of video data, the method comprising:down-sampling a reconstructed luma block to obtain a down-sampled lumablock, the reconstructed luma block corresponding to a chroma block;obtaining first down-sampled samples of reconstructed top neighboringluma samples that are above the reconstructed luma block or seconddown-sampled samples of reconstructed left neighboring luma samples thatare left to the reconstructed luma block, wherein the reconstructed topneighboring luma samples are within a single row being adjacent to thereconstructed luma block; deriving, parameters of a linear model (LM),based on the first or second down-sampled samples and reconstructedneighboring chroma samples that are above the chroma block orreconstructed neighboring chroma samples that are left to the chromablock; and generating predicted chroma values of the chroma block basedon the parameters of the LM and the down-sampled luma block.

In an embodiment, the disclosure includes a method for cross-componentprediction of a block of video data, the method comprising:down-sampling a reconstructed luma block to obtain a down-sampled lumablock, the reconstructed luma block corresponding to a chroma block;obtaining first down-sampled samples of reconstructed top neighboringluma samples that are above (immediately above) the reconstructed lumablock and second down-sampled samples of reconstructed left neighboringluma samples that are left to the reconstructed luma block, wherein thereconstructed top neighboring luma samples are within a single row beingadjacent to the reconstructed luma block; deriving, parameters of alinear model (LM), based on the first down-sampled samples and thesecond down-sampled samples, and reconstructed neighboring chromasamples that are above the chroma block and reconstructed neighboringchroma samples that are left to the chroma block; and generatingpredicted chroma values of the chroma block based on the parameters ofthe LM and the down-sampled luma block.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the first down-sampled luma samples areobtained by down-sampling on the reconstructed top neighboring lumasamples being within the single row.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the second down-sampled luma samples areobtained by down-sampling on the reconstructed left neighboring lumasamples.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the reconstructed left neighboring lumasamples are within N columns which are left to the reconstructed lumablock, wherein 0<N<=3 and N is a positive integer.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the reconstructed left neighboring lumasamples are within a single column which is left (immediately left) tothe reconstructed luma block.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the linear model (LM) comprises one or moreof the following linear model of: cross-component linear model (CCLM)mode, multi-directional linear model (MDLM) mode, and multiple modellinear model (MMLM) mode.

In an embodiment, the disclosure includes a method for cross-componentprediction of a block of video data, the method comprising:down-sampling a reconstructed luma block to obtain a down-sampled lumablock, the reconstructed luma block corresponding to a chroma block;determining a max luma value and a min luma value based on firstdown-sampled samples of reconstructed top neighboring luma samples thatare above the reconstructed luma block or second down-sampled samples ofreconstructed left neighboring luma samples that are left to thereconstructed luma block, wherein the reconstructed top neighboring lumasamples are within a single row being adjacent to the reconstructed lumablock; determining a first chroma value and a second chroma value basedon reconstructed neighboring chroma samples of the chroma block, whereinthe first chroma value and the second chroma value are respectivelyassociated with the max luma value and min luma value; deriving,parameters of a linear model (LM) based on the max luma value and themin luma value and the first chroma value and the second chroma value;and generating predicted chroma values of the chroma block based on theparameters of the LM and the down-sampled luma block.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the max luma value is determined based onvalues of one or more first down-sampled samples that are larger thanvalues of rest of the first down-sampled samples; or the min luma valueis obtained based on values of one or more first down-sampled samplesthat are smaller than values of rest of the first down-sampled samples;or the max luma value is determined based on values of one or moresecond down-sampled samples that are larger than values of rest of thesecond down-sampled samples; or the min luma value is obtained based onvalues of one or more second down-sampled samples that are smaller thanvalues of rest of the second down-sampled samples.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the first chroma value is determined basedon values of one or more reconstructed neighboring chroma samples,wherein the one or more reconstructed neighboring chroma samplescorresponds to the one or more first down-sampled samples whose valuesare larger than values of rest of the first down-sampled samples, and/orthe second chroma value is determined based on values of one or morereconstructed neighboring chroma samples, wherein the one or morereconstructed neighboring chroma samples correspond to the one or morefirst down-sampled samples whose values are smaller than values of restof the first down-sampled samples.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the first chroma value is determined basedon values of one or more reconstructed neighboring chroma samples,wherein the one or more reconstructed neighboring chroma samplescorresponds to the one or more second down-sampled samples whose valuesare larger than values of rest of the second down-sampled samples,and/or the second chroma value is determined based on values of one ormore reconstructed neighboring chroma samples, wherein the one or morereconstructed neighboring chroma samples correspond to the one or moresecond down-sampled samples whose values are smaller than values of restof the second down-sampled samples.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the determining a first chroma value and asecond chroma value based on reconstructed neighboring chroma samples ofthe chroma block, comprises: determining, from the reconstructedneighboring chroma samples of the chroma block, a first chroma value anda second chroma value respectively corresponding to the max luma valueand min luma value.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the first down-sampled samples are obtainedby down-sampling on the reconstructed top neighboring luma samples whichare within the single row being adjacent to the reconstructed lumablock.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the second down-sampled samples areobtained by down-sampling on the reconstructed left neighboring lumasamples.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the reconstructed left neighboring lumasamples are within N columns which are left to the reconstructed lumablock, wherein 0<N<=3 and N is a positive integer.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the reconstructed left neighboring lumasamples are within a single column which are left to the reconstructedluma block.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the linear model (LM) comprises one or moreof the following linear model of: cross-component linear model (CCLM)mode, multi-directional linear model (MDLM) mode, and multiple modellinear model (MMLM) mode.

In an embodiment, the disclosure includes a method for cross-componentprediction of a block of video data, the method comprising:down-sampling a reconstructed luma block to obtain a down-sampled lumablock, the reconstructed luma block corresponding to a chroma block;determining a max luma value and a min luma value based on firstdown-sampled samples of reconstructed top neighboring luma samples thatare above the reconstructed luma block and second down-sampled samplesof reconstructed left neighboring luma samples that are left to thereconstructed luma block, wherein the reconstructed top neighboring lumasamples are within a single row being adjacent to the reconstructed lumablock; determining a first chroma value and a second chroma value basedon reconstructed neighboring chroma samples of the chroma block, whereinthe first chroma value and the second chroma value are respectivelyassociated with the max luma value and min luma value; deriving,parameters of a linear model (LM) based on the max luma value and themin luma value and the first chroma value and the second chroma value;and generating predicted chroma values of the chroma block based on theparameters of the LM and the down-sampled luma block.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the max luma value is determined based onvalues of one or more first and second down-sampled samples that arelarger than values of rest of the first and second down-sampled samples;or the min luma value is determined based on values of one or more firstand second down-sampled samples that are smaller than values of rest ofthe first and second down-sampled samples.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the first chroma value is determined basedon values of one or more reconstructed neighboring chroma samples,wherein the one or more reconstructed neighboring chroma samplescorresponds to the one or more first and second down-sampled sampleswhose values are larger than values of rest of the first and seconddown-sampled samples, or the second chroma value is determined based onvalues of one or more reconstructed neighboring chroma samples, whereinthe one or more reconstructed neighboring chroma samples correspond tothe one or more first and second down-sampled samples whose values aresmaller than values of rest of the first and second down-sampledsamples.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the determining a first chroma value and asecond chroma value based on reconstructed neighboring chroma samples ofthe chroma block, comprises: determining, from the reconstructedneighboring chroma samples of the chroma block, a first chroma value anda second chroma value respectively corresponding to the max luma valueand min luma value.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the first down-sampled samples are obtainedby down-sampling on the reconstructed top neighboring luma samples whichare within a single row being adjacent to the reconstructed luma block.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the second down-sampled samples areobtained by down-sampling on the reconstructed left neighboring lumasamples.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the reconstructed left neighboring lumasamples are within N columns which are left to the reconstructed lumablock, wherein 0<N<=3 and N is a positive integer.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the reconstructed left neighboring lumasamples are within a single column which are left to the reconstructedluma block.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the linear model (LM) comprises one or moreof the following linear model of: cross-component linear model (CCLM)mode, multi-directional linear model (MDLM) mode, and multiple modellinear model (MMLM) mode.

In an embodiment, the disclosure includes an apparatus forcross-component prediction of a block of video data, the apparatuscomprising: a processor and a memory with stored instructions which whenexecuted by the processor cause the processor to: down-sample areconstructed luma block to obtain a down-sampled luma block, thereconstructed luma block corresponding to a chroma block; obtain firstdown-sampled samples of reconstructed top neighboring luma samples thatare above the reconstructed luma block or second down-sampled samples ofreconstructed left neighboring luma samples that are left to thereconstructed luma block, wherein the reconstructed top neighboring lumasamples are within a single row being adjacent to the reconstructed lumablock; derive, parameters of a linear model (LM), based on the first orsecond down-sampled samples and reconstructed neighboring chroma samplesthat are above the chroma block or reconstructed neighboring chromasamples that are left to the chroma block; and generate predicted chromavalues of the chroma block based on the parameters of the LM and thedown-sampled luma block.

In an embodiment, the disclosure includes an apparatus forcross-component prediction of a block of video data, the apparatuscomprising: a processor and a memory with stored instructions which whenexecuted by the processor cause the processor to: down-sample areconstructed luma block to obtain a down-sampled luma block, thereconstructed luma block corresponding to a chroma block; obtain firstdown-sampled samples of reconstructed top neighboring luma samples thatare above (immediately above) the reconstructed luma block and seconddown-sampled samples of reconstructed left neighboring luma samples thatare left to the reconstructed luma block, wherein the reconstructed topneighboring luma samples are within a single row being adjacent to thereconstructed luma block; derive, parameters of a linear model (LM),based on the first down-sampled samples and the second down-sampledsamples, and reconstructed neighboring chroma samples that are above thechroma block and reconstructed neighboring chroma samples that are leftto the chroma block; and generate predicted chroma values of the chromablock based on the parameters of the LM and the down-sampled luma block.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the first down-sampled luma samples areobtained by down-sampling on the reconstructed top neighboring lumasamples being within the single row.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the second down-sampled luma samples areobtained by down-sampling on the reconstructed left neighboring lumasamples.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the reconstructed left neighboring lumasamples are within N columns which are left to the reconstructed lumablock, wherein 0<N<=3 and N is a positive integer.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the reconstructed left neighboring lumasamples are within a single column which is left (immediately left) tothe reconstructed luma block.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the linear model (LM) comprises one or moreof the following linear model of: cross-component linear model (CCLM)mode, multi-directional linear model (MDLM) mode, and multiple modellinear model (MMLM) mode.

In an embodiment, the disclosure includes an apparatus forcross-component prediction of a block of video data, the apparatuscomprising: a processor and a memory with stored instructions which whenexecuted by the processor cause the processor to: down-sample areconstructed luma block to obtain a down-sampled luma block, thereconstructed luma block corresponding to a chroma block; determine amax luma value and a min luma value based on first down-sampled samplesof reconstructed top neighboring luma samples that are above thereconstructed luma block or second down-sampled samples of reconstructedleft neighboring luma samples that are left to the reconstructed lumablock, wherein the reconstructed top neighboring luma samples are withina single row being adjacent to the reconstructed luma block; determine afirst chroma value and a second chroma value based on reconstructedneighboring chroma samples of the chroma block, wherein the first chromavalue and the second chroma value are respectively associated with themax luma value and min luma value; derive, parameters of a linear model(LM) based on the max luma value and the min luma value and the firstchroma value and the second chroma value; and generate predicted chromavalues of the chroma block based on the parameters of the LM and thedown-sampled luma block.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the max luma value is determined based onvalues of one or more first down-sampled samples that are larger thanvalues of rest of the first down-sampled samples; or the min luma valueis obtained based on values of one or more first down-sampled samplesthat are smaller than values of rest of the first down-sampled samples;or, the max luma value is determined based on values of one or moresecond down-sampled samples that are larger than values of rest of thesecond down-sampled samples; or the min luma value is obtained based onvalues of one or more second down-sampled samples that are smaller thanvalues of rest of the second down-sampled samples.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the first chroma value is determined basedon values of one or more reconstructed neighboring chroma samples,wherein the one or more reconstructed neighboring chroma samplescorresponds to the one or more first down-sampled samples whose valuesare larger than values of rest of the first down-sampled samples, and/orthe second chroma value is determined based on values of one or morereconstructed neighboring chroma samples, wherein the one or morereconstructed neighboring chroma samples correspond to the one or morefirst down-sampled samples whose values are smaller than values of restof the first down-sampled samples.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the first chroma value is determined basedon values of one or more reconstructed neighboring chroma samples,wherein the one or more reconstructed neighboring chroma samplescorresponds to the one or more second down-sampled samples whose valuesare larger than values of rest of the second down-sampled samples,and/or the second chroma value is determined based on values of one ormore reconstructed neighboring chroma samples, wherein the one or morereconstructed neighboring chroma samples correspond to the one or moresecond down-sampled samples whose values are smaller than values of restof the second down-sampled samples.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the determine a first chroma value and asecond chroma value based on reconstructed neighboring chroma samples ofthe chroma block, comprises: determine, from the reconstructedneighboring chroma samples of the chroma block, a first chroma value anda second chroma value respectively corresponding to the max luma valueand min luma value.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the first down-sampled samples are obtainedby down-sampling on the reconstructed top neighboring luma samples whichare within the single row being adjacent to the reconstructed lumablock.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the second down-sampled samples areobtained by down-sampling on the reconstructed left neighboring lumasamples.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the reconstructed left neighboring lumasamples are within N columns which are left to the reconstructed lumablock, wherein 0<N<=3 and N is a positive integer.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the reconstructed left neighboring lumasamples are within a single column which are left to the reconstructedluma block.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the linear model (LM) comprises one or moreof the following linear model of: cross-component linear model (CCLM)mode, multi-directional linear model (MDLM) mode, and multiple modellinear model (MMLM) mode.

In an embodiment, the disclosure includes an apparatus forcross-component prediction of a block of video data, the apparatuscomprising: a processor and a memory with stored instructions which whenexecuted by the processor cause the processor to: down-sample areconstructed luma block to obtain a down-sampled luma block, thereconstructed luma block corresponding to a chroma block; determine amax luma value and a min luma value based on first down-sampled samplesof reconstructed top neighboring luma samples that are above thereconstructed luma block and second down-sampled samples ofreconstructed left neighboring luma samples that are left to thereconstructed luma block, wherein the reconstructed top neighboring lumasamples are within a single row being adjacent to the reconstructed lumablock; determine a first chroma value and a second chroma value based onreconstructed neighboring chroma samples of the chroma block, whereinthe first chroma value and the second chroma value are respectivelyassociated with the max luma value and min luma value; derive,parameters of a linear model (LM) based on the max luma value and themin luma value and the first chroma value and the second chroma value;and generate predicted chroma values of the chroma block based on theparameters of the LM and the down-sampled luma block.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the max luma value is determined based onvalues of one or more first and second down-sampled samples that arelarger than values of rest of the first and second down-sampled samples;or the min luma value is determined based on values of one or more firstand second down-sampled samples that are smaller than values of rest ofthe first and second down-sampled samples.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the first chroma value is determined basedon values of one or more reconstructed neighboring chroma samples,wherein the one or more reconstructed neighboring chroma samplescorresponds to the one or more first and second down-sampled sampleswhose values are larger than values of rest of the first and seconddown-sampled samples, or the second chroma value is determined based onvalues of one or more reconstructed neighboring chroma samples, whereinthe one or more reconstructed neighboring chroma samples correspond tothe one or more first and second down-sampled samples whose values aresmaller than values of rest of the first and second down-sampledsamples.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the determine a first chroma value and asecond chroma value based on reconstructed neighboring chroma samples ofthe chroma block, comprises: determine, from the reconstructedneighboring chroma samples of the chroma block, a first chroma value anda second chroma value respectively corresponding to the max luma valueand min luma value.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the first down-sampled samples are obtainedby down-sampling on the reconstructed top neighboring luma samples whichare within a single row being adjacent to the reconstructed luma block.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the second down-sampled samples areobtained by down-sampling on the reconstructed left neighboring lumasamples.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the reconstructed left neighboring lumasamples are within N columns which are left to the reconstructed lumablock, wherein 0<N<=3 and N is a positive integer.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the reconstructed left neighboring lumasamples are within a single column which are left to the reconstructedluma block.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the linear model (LM) comprises one or moreof the following linear model of: cross-component linear model (CCLM)mode, multi-directional linear model (MDLM) mode, and multiple modellinear model (MMLM) mode.

In an embodiment, the disclosure includes an electronic device forcoding/decoding video data, the electronic device comprising one or moreprocessing units configured to perform any one of the preceding aspects.

In an embodiment, the disclosure includes a computer readable mediumstoring instructions which when executed on a processor cause theprocessor to perform the method according to any of the precedingaspects.

For the purpose of clarity, any one of the foregoing embodiments may becombined with any one or more of the other foregoing embodiments tocreate a new embodiment within the scope of the present disclosure.

These and other features will be more clearly understood from thefollowing detailed description taken in conjunction with theaccompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this disclosure, reference is nowmade to the following brief description, taken in connection with theaccompanying drawings and detailed description, wherein like referencenumerals represent like parts.

FIG. 1 is a flowchart of an example method of coding a video signal.

FIG. 2 is a schematic diagram of an example coding and decoding (codec)system for video coding.

FIG. 3 is a schematic diagram illustrating an example video encoder thatmay perform cross-component intra-prediction.

FIG. 4 is a schematic diagram illustrating an example video decoder thatmay perform cross-component intra-prediction.

FIG. 5 is a schematic diagram illustrating an example ofintra-prediction modes.

FIG. 6 is a schematic diagram illustrating an example mechanism ofperforming cross-component intra-prediction.

FIG. 7 is a schematic diagram illustrating an example mechanism ofperforming cross-component linear model (CCLM) intra-prediction.

FIG. 8 is a graph illustrating an example mechanism of determininglinear model parameters to support CCLM intra-prediction.

FIGS. 9-10 are schematic diagrams illustrating an example mechanism ofperforming multi-directional linear model (MDLM) intra-prediction.

FIG. 11 is a graph illustrating an example mechanism of determininglinear model parameters to support multiple model CCLM (MMLM)intra-prediction.

FIGS. 12-15 are schematic diagrams illustrating example mechanisms ofdown-sampling to support cross-component intra-prediction.

FIG. 16 is a flowchart of an example method of employing down-samplingwhile performing cross-component intra-prediction at an encoder.

FIG. 17 is a flowchart of an example method of employing down-samplingwhile performing cross-component intra-prediction at a decoder.

FIG. 18 is a schematic diagram of an example video coding device.

FIG. 19 is a schematic diagram of an example system for employingdown-sampling while performing cross-component intra-prediction.

FIG. 20 is an illustration of top template and left template.

FIG. 21 is an illustration of reference samples.

DETAILED DESCRIPTION

It should be understood at the outset that although an illustrativeimplementation of one or more embodiments are provided below, thedisclosed systems and/or methods may be implemented using any number oftechniques, whether currently known or in existence. The disclosureshould in no way be limited to the illustrative implementations,drawings, and techniques illustrated below, including the exemplarydesigns and implementations illustrated and described herein, but may bemodified within the scope of the appended claims along with their fullscope of equivalents.

Video coding includes partitioning video frames into blocks and encodingthe blocks via intra-prediction and inter-prediction to compress thesize of a video file. Specifically, the video frames can be partitionedinto coding units (CUs) that contain luma coding blocks (CBs) and chromaCBs (light values and color values, respectively). Prediction (intra orinter) can then be applied to determine reference blocks for the codingblocks. Prediction results in prediction information that codes the CBsby reference to the reference block(s). Samples (e.g., pixels) of theCBs are compared to samples of the reference block(s) and differences invalues are maintained as residual samples. Intra-prediction selectsreference blocks in the same frame as the current block, whileinter-prediction selects reference blocks in different frames from thecurrent block. In most cases, intra-prediction modes employ referenceluma blocks to predict luma blocks and reference chroma blocks topredict chroma blocks. Cross-component modes may also be used. Incross-component intra-prediction, luma reference samples are employed topredict chroma samples in a current block.

The present disclosure relates to improvements in the process ofperforming cross-component intra-prediction. Specifically, a luma blockgenerally contains four times the number of samples of a correspondingchroma block. As such, the luma reference blocks are down-sampled tomatch the resolution of the chroma block to support accuratecross-component intra-prediction. Down-sampling is the process ofreducing the resolution of a group of pixel samples. Certain mechanismsof down-sampling use significant memory resources without providingsignificant benefits in accuracy. Specifically, certain down-samplingmechanisms use multiple rows and columns of reference samples togenerate a single row/column of down-sampled reference samples for usein cross-component intra-prediction.

Disclosed herein are improved down-sampling mechanisms to supportincreased efficiency of cross-component intra-prediction.Cross-component intra-prediction may include CCLM mode intra-prediction,MDLM mode intra-prediction, and/or MMLM mode intra-prediction. Toperform such intra-prediction, luma samples in the same CU and lumasamples and chroma samples from neighboring CBs are used as referencesamples to predict chroma samples in a current block. In the presentdisclosure, a single row and/or a single column of neighboring referencesamples can be used during down-sampling to create a single row and/orcolumn of down-sampled neighboring reference samples. The resultingdown-sampled neighboring reference samples are generally as accurate asreference samples down-sampled from multiple rows/columns. However,using a single row and/or column for down-sampling significantly reducesthe amount of line buffer memory used for the intra-prediction process.Accordingly, using a single row and/or column for down-sampling theneighboring luma reference samples decreases resource usage withoutsignificantly reducing the coding efficiency of the cross-componentintra-prediction mechanisms.

FIG. 1 is a flowchart of an example operating method 100 of coding avideo signal. Specifically, a video signal is encoded at an encoder. Theencoding process compresses the video signal by employing variousmechanisms to reduce the video file size. A smaller file size allows thecompressed video file to be transmitted toward a user, while reducingassociated bandwidth overhead. The decoder then decodes the compressedvideo file to reconstruct the original video signal for display to anend user. The decoding process generally mirrors the encoding process toallow the decoder to consistently reconstruct the video signal.

At step 101, the video signal is input into the encoder. For example,the video signal may be an uncompressed video file stored in memory. Asanother example, the video file may be captured by a video capturedevice, such as a video camera, and encoded to support live streaming ofthe video. The video file may include both an audio component and avideo component. The video component contains a series of image framesthat, when viewed in a sequence, gives the visual impression of motion.The frames contain pixels that are expressed in terms of light, referredto herein as luma components (or luma samples), and color, which isreferred to as chroma components (or color samples). In some examples,the frames may also contain depth values to support three dimensionalviewing.

At step 103, the video is partitioned into blocks. Partitioning includessubdividing the pixels in each frame into square and/or rectangularblocks for compression. For example, in High Efficiency Video Coding(HEVC) (also known as H.265 and MPEG-H Part 2) the frame can first bedivided into coding tree units (CTUs), which are blocks of a predefinedsize (e.g., sixty four pixels by sixty four pixels). The CTUs containboth luma and chroma samples. Coding trees may be employed to divide theCTUs into blocks and then recursively subdivide the blocks untilconfigurations are achieved that support further encoding. For example,luma components of a frame may be subdivided until the individual blockscontain relatively homogenous lighting values. Further, chromacomponents of a frame may be subdivided until the individual blockscontain relatively homogenous color values. Accordingly, partitioningmechanisms vary depending on the content of the video frames.

At step 105, various compression mechanisms are employed to compress theimage blocks partitioned at step 103. For example, inter-predictionand/or intra-prediction may be employed. Inter-prediction is designed totake advantage of the fact that objects in a common scene tend to appearin successive frames. Accordingly, a block depicting an object in areference frame need not be repeatedly described in adjacent frames.Specifically, an object, such as a table, may remain in a constantposition over multiple frames. Hence the table is described once andadjacent frames can refer back to the reference frame. Pattern matchingmechanisms may be employed to match objects over multiple frames.Further, moving objects may be represented across multiple frames, forexample due to object movement or camera movement. As a particularexample, a video may show an automobile that moves across the screenover multiple frames. Motion vectors can be employed to describe suchmovement. A motion vector is a two-dimensional vector that provides anoffset from the coordinates of an object in a frame to the coordinatesof the object in a reference frame. As such, inter-prediction can encodean image block in a current frame as a set of motion vectors indicatingan offset from a corresponding block in a reference frame.

Intra-prediction encodes blocks in a common frame. Intra-predictiontakes advantage of the fact that luma and chroma components tend tocluster in a frame. For example, a patch of green in a portion of a treetends to be positioned adjacent to similar patches of green.Intra-prediction employs multiple directional prediction modes (e.g.,thirty three in HEVC), a planar mode, and a direct current (DC) mode.The directional modes indicate that a current block is similar/the sameas samples of a neighbor block in a corresponding direction. Planar modeindicates that a series of blocks along a row/column (e.g., a plane) canbe interpolated based on neighbor blocks at the edges of the row. Planarmode, in effect, indicates a smooth transition of light/color across arow/column by employing a relatively constant slope in changing values.DC mode is employed for boundary smoothing and indicates that a block issimilar/the same as an average value associated with samples of all theneighbor blocks associated with the angular directions of thedirectional prediction modes. Accordingly, intra-prediction blocks canrepresent image blocks as various relational prediction mode valuesinstead of the actual values. Further, inter-prediction blocks canrepresent image blocks as motion vector values instead of the actualvalues. In either case, the prediction blocks may not exactly representthe image blocks in some cases. Any differences are stored in residualblocks. Transforms may be applied to the residual blocks to furthercompress the file.

At step 107, various filtering techniques may be applied. In HEVC, thefilters are applied according to an in-loop filtering scheme. The blockbased prediction discussed above may result in the creation of blockyimages at the decoder. Further, the block based prediction scheme mayencode a block and then reconstruct the encoded block for later use as areference block. The in-loop filtering scheme iteratively applies noisesuppression filters, de-blocking filters, adaptive loop filters, andsample adaptive offset (SAO) filters to the blocks/frames. These filtersmitigate such blocking artifacts so that the encoded file can beaccurately reconstructed. Further, these filters mitigate artifacts inthe reconstructed reference blocks so that artifacts are less likely tocreate additional artifacts in subsequent blocks that are encoded basedon the reconstructed reference blocks.

Once the video signal has been partitioned, compressed, and filtered,the resulting data is encoded in a bitstream at step 109. The bitstreamincludes the data discussed above as well as any signaling data desiredto support proper video signal reconstruction at the decoder. Forexample, such data may include partition data, prediction data, residualblocks, and various flags providing coding instructions to the decoder.The bitstream may be stored in memory for transmission toward a decoderupon request. The bitstream may also be broadcast and/or multicasttoward a plurality of decoders. The creation of the bitstream is aniterative process. Accordingly, steps 101, 103, 105, 107, and 109 mayoccur continuously and/or simultaneously over many frames and blocks.The order shown in FIG. 1 is presented for clarity and ease ofdiscussion, and is not intended to limit the video coding process to aparticular order.

The decoder receives the bitstream and begins the decoding process atstep 111. Specifically, the decoder employs an entropy decoding schemeto convert the bitstream into corresponding syntax and video data. Thedecoder employs the syntax data from the bitstream to determine thepartitions for the frames at step 111. The partitioning should match theresults of block partitioning at step 103. Entropy encoding/decoding asemployed in step 111 is now described. The encoder makes many choicesduring the compression process, such as selecting block partitioningschemes from several possible choices based on the spatial positioningof values in the input image(s). Signaling the exact choices may employa large number of bins. As used herein, a bin is a binary value that istreated as a variable (e.g., a bit value that may vary depending oncontext). Entropy coding allows the encoder to discard any options thatare clearly not viable for a particular case, leaving a set of allowableoptions. Each allowable option is then assigned a code word. The lengthof the code word is based on the number of allowable options (e.g., onebin for two options, two bins for three to four options, etc.) Theencoder then encodes the code word for the selected option. This schemereduces the size of the code words as the code words are as big asdesired to uniquely indicate a selection from a small sub-set ofallowable options as opposed to uniquely indicating the selection from apotentially large set of all possible options. The decoder then decodesthe selection by determining the set of allowable options in a similarmanner to the encoder. By determining the set of allowable options, thedecoder can read the code word and determine the selection made by theencoder.

At step 113, the decoder performs block decoding. Specifically, thedecoder employs reverse transforms to generate residual blocks. Then thedecoder employs the residual blocks and corresponding prediction blocksto reconstruct the image blocks according to the partitioning. Theprediction blocks may include both intra-prediction blocks andinter-prediction blocks as generated at the encoder at step 105. Thereconstructed image blocks are then positioned into frames of areconstructed video signal according to the partitioning data determinedat step 111. Syntax for step 113 may also be signaled in the bitstreamvia entropy coding as discussed above.

At step 115, filtering is performed on the frames of the reconstructedvideo signal in a manner similar to step 107 at the encoder. Forexample, noise suppression filters, de-blocking filters, adaptive loopfilters, and SAO filters may be applied to the frames to remove blockingartifacts. Once the frames are filtered, the video signal can be outputto a display at step 117 for viewing by an end user.

The present disclosure relates to modifications to down-samplingmechanisms to support intra-prediction to reduce resource usage withoutsignificantly reducing accuracy, and hence coding efficiency whencompressing blocks. Hence, the present disclosure improves thefunctionality of block compression at step 105 at the encoder and blockdecoding at step 113 at the decoder. Specifically, at steps 105 and 113,a single row of luma samples are down-sampled and then employed forcross-component intra-prediction.

FIG. 2 is a schematic diagram of an example coding and decoding (codec)system 200 for video coding. Specifically, codec system 200 providesfunctionality to support the implementation of operating method 100.Codec system 200 is generalized to depict components employed in both anencoder and a decoder. Codec system 200 receives and partitions a videosignal as discussed with respect to steps 101 and 103 in operatingmethod 100, which results in a partitioned video signal 201. Codecsystem 200 then compresses the partitioned video signal 201 into a codedbitstream when acting as an encoder as discussed with respect to steps105, 107, and 109 in method 100. When acting as a decoder codec system200 generates an output video signal from the bitstream as discussedwith respect to steps 111, 113, 115, and 117 in operating method 100.The codec system 200 includes a general coder control component 211, atransform scaling and quantization component 213, an intra-pictureestimation component 215, an intra-picture prediction component 217, amotion compensation component 219, a motion estimation component 221, ascaling and inverse transform component 229, a filter control analysiscomponent 227, an in-loop filters component 225, a decoded picturebuffer component 223, and a header formatting and context adaptivebinary arithmetic coding (CABAC) component 231. Such components arecoupled as shown. In FIG. 2, black lines indicate movement of data to beencoded/decoded while dashed lines indicate movement of control datathat controls the operation of other components. The components of codecsystem 200 may all be present in the encoder. The decoder may include asubset of the components of codec system 200. For example, the decodermay include the intra-picture prediction component 217, the motioncompensation component 219, the scaling and inverse transform component229, the in-loop filters component 225, and the decoded picture buffercomponent 223. These components are now described.

The partitioned video signal 201 is a captured video sequence that hasbeen partitioned into blocks of pixels by a coding tree. A coding treeemploys various split modes to subdivide a block of pixels into smallerblocks of pixels. These blocks can then be further subdivided intosmaller blocks. The blocks may be referred to as nodes on the codingtree. Larger parent nodes are split into smaller child nodes. The numberof times a node is subdivided is referred to as the depth of thenode/coding tree. The divided blocks can be included in coding units(CUs) in some cases. For example, a CU can be a sub-portion of a CTUthat contains a luma block, red difference chroma (Cr) block(s), and ablue difference chroma (Cb) block(s) along with corresponding syntaxinstructions for the CU. The split modes may include a binary tree (BT),triple tree (TT), and a quad tree (QT) employed to partition a node intotwo, three, or four child nodes, respectively, of varying shapesdepending on the split modes employed. The partitioned video signal 201is forwarded to the general coder control component 211, the transformscaling and quantization component 213, the intra-picture estimationcomponent 215, the filter control analysis component 227, and the motionestimation component 221 for compression.

The general coder control component 211 is configured to make decisionsrelated to coding of the images of the video sequence into the bitstreamaccording to application constraints. For example, the general codercontrol component 211 manages optimization of bitrate/bitstream sizeversus reconstruction quality. Such decisions may be made based onstorage space/bandwidth availability and image resolution requests. Thegeneral coder control component 211 also manages buffer utilization inlight of transmission speed to mitigate buffer underrun and overrunissues. To manage these issues, the general coder control component 211manages partitioning, prediction, and filtering by the other components.For example, the general coder control component 211 may dynamicallyincrease compression complexity to increase resolution and increasebandwidth usage or decrease compression complexity to decreaseresolution and bandwidth usage. Hence, the general coder controlcomponent 211 controls the other components of codec system 200 tobalance video signal reconstruction quality with bit rate concerns. Thegeneral coder control component 211 creates control data, which controlsthe operation of the other components. The control data is alsoforwarded to the header formatting and CABAC component 231 to be encodedin the bitstream to signal parameters for decoding at the decoder.

The partitioned video signal 201 is also sent to the motion estimationcomponent 221 and the motion compensation component 219 forinter-prediction. A frame or slice of the partitioned video signal 201may be divided into multiple video blocks. Motion estimation component221 and the motion compensation component 219 perform inter-predictivecoding of the received video block relative to one or more blocks in oneor more reference frames to provide temporal prediction. Codec system200 may perform multiple coding passes, e.g., to select an appropriatecoding mode for each block of video data.

Motion estimation component 221 and motion compensation component 219may be highly integrated, but are illustrated separately for conceptualpurposes. Motion estimation, performed by motion estimation component221, is the process of generating motion vectors, which estimate motionfor video blocks. A motion vector, for example, may indicate thedisplacement of a coded object relative to a predictive block. Apredictive block is a block that is found to closely match the block tobe coded, in terms of pixel difference. A predictive block may also bereferred to as a reference block. Such pixel difference may bedetermined by sum of absolute difference (SAD), sum of square difference(SSD), or other difference metrics. HEVC employs several coded objectsincluding a CTU, coding tree blocks (CTBs), and CUs. For example, a CTUcan be divided into CTBs, which can then be divided into CBs forinclusion in CUs. A CU can be encoded as a prediction unit (PU)containing prediction data and/or one or more transform unit (TUs)containing transformed residual data for the CU. The motion estimationcomponent 221 generates motion vectors, PUs, and TUs by using arate-distortion analysis as part of a rate distortion optimizationprocess. For example, the motion estimation component 221 may determinemultiple reference blocks, multiple motion vectors, etc. for a currentblock/frame, and may select the reference blocks, motion vectors, etc.having the best rate-distortion characteristics. The bestrate-distortion characteristics balance both quality of videoreconstruction (e.g., amount of data loss by compression) with codingefficiency (e.g., size of the final encoding).

In some examples, codec system 200 may calculate values for sub-integerpixel positions of reference pictures stored in decoded picture buffercomponent 223. For example, video codec system 200 may interpolatevalues of one-quarter pixel positions, one-eighth pixel positions, orother fractional pixel positions of the reference picture. Therefore,motion estimation component 221 may perform a motion search relative tothe full pixel positions and fractional pixel positions and output amotion vector with fractional pixel precision. The motion estimationcomponent 221 calculates a motion vector for a PU of a video block in aninter-coded slice by comparing the position of the PU to the position ofa predictive block of a reference picture. Motion estimation component221 outputs the calculated motion vector as motion data to headerformatting and CABAC component 231 for encoding and motion to the motioncompensation component 219.

Motion compensation, performed by motion compensation component 219, mayinvolve fetching or generating the predictive block based on the motionvector determined by motion estimation component 221. Again, motionestimation component 221 and motion compensation component 219 may befunctionally integrated, in some examples. Upon receiving the motionvector for the PU of the current video block, motion compensationcomponent 219 may locate the predictive block to which the motion vectorpoints. A residual video block is then formed by subtracting pixelvalues of the predictive block from the pixel values of the currentvideo block being coded, forming pixel difference values. In general,motion estimation component 221 performs motion estimation relative toluma components, and motion compensation component 219 uses motionvectors calculated based on the luma components for both chromacomponents and luma components. The predictive block and residual blockare forwarded to transform scaling and quantization component 213.

The partitioned video signal 201 is also sent to intra-pictureestimation component 215 and intra-picture prediction component 217. Aswith motion estimation component 221 and motion compensation component219, intra-picture estimation component 215 and intra-picture predictioncomponent 217 may be highly integrated, but are illustrated separatelyfor conceptual purposes. The intra-picture estimation component 215 andintra-picture prediction component 217 intra-predict a current blockrelative to blocks in a current frame, as an alternative to theinter-prediction performed by motion estimation component 221 and motioncompensation component 219 between frames, as described above. Inparticular, the intra-picture estimation component 215 determines anintra-prediction mode to use to encode a current block. In someexamples, intra-picture estimation component 215 selects an appropriateintra-prediction mode to encode a current block from multiple testedintra-prediction modes. The selected intra-prediction modes are thenforwarded to the header formatting and CABAC component 231 for encoding.

For example, the intra-picture estimation component 215 calculatesrate-distortion values using a rate-distortion analysis for the varioustested intra-prediction modes, and selects the intra-prediction modehaving the best rate-distortion characteristics among the tested modes.Rate-distortion analysis generally determines an amount of distortion(or error) between an encoded block and an original unencoded block thatwas encoded to produce the encoded block, as well as a bitrate (e.g., anumber of bits) used to produce the encoded block. The intra-pictureestimation component 215 calculates ratios from the distortions andrates for the various encoded blocks to determine which intra-predictionmode exhibits the best rate-distortion value for the block. In addition,intra-picture estimation component 215 may be configured to code depthblocks of a depth map using a depth modeling mode (DMM) based onrate-distortion optimization (RDO).

The intra-picture prediction component 217 may generate a residual blockfrom the predictive block based on the selected intra-prediction modesdetermined by intra-picture estimation component 215 when implemented onan encoder or read the residual block from the bitstream whenimplemented on a decoder. The residual block includes the difference invalues between the predictive block and the original block, representedas a matrix. The residual block is then forwarded to the transformscaling and quantization component 213. The intra-picture estimationcomponent 215 and the intra-picture prediction component 217 may operateon both luma and chroma components.

The transform scaling and quantization component 213 is configured tofurther compress the residual block. The transform scaling andquantization component 213 applies a transform, such as a discretecosine transform (DCT), a discrete sine transform (DST), or aconceptually similar transform, to the residual block, producing a videoblock comprising residual transform coefficient values. Wavelettransforms, integer transforms, sub-band transforms or other types oftransforms could also be used. The transform may convert the residualinformation from a pixel value domain to a transform domain, such as afrequency domain. The transform scaling and quantization component 213is also configured to scale the transformed residual information, forexample based on frequency. Such scaling involves applying a scalefactor to the residual information so that different frequencyinformation is quantized at different granularities, which may affectfinal visual quality of the reconstructed video. The transform scalingand quantization component 213 is also configured to quantize thetransform coefficients to further reduce bit rate. The quantizationprocess may reduce the bit depth associated with some or all of thecoefficients. The degree of quantization may be modified by adjusting aquantization parameter. In some examples, the transform scaling andquantization component 213 may then perform a scan of the matrixincluding the quantized transform coefficients. The quantized transformcoefficients are forwarded to the header formatting and CABAC component231 to be encoded in the bitstream.

The scaling and inverse transform component 229 applies a reverseoperation of the transform scaling and quantization component 213 tosupport motion estimation. The scaling and inverse transform component229 applies inverse scaling, transformation, and/or quantization toreconstruct the residual block in the pixel domain, e.g., for later useas a reference block which may become a predictive block for anothercurrent block. The motion estimation component 221 and/or motioncompensation component 219 may calculate a reference block by adding theresidual block back to a corresponding predictive block for use inmotion estimation of a later block/frame. Filters are applied to thereconstructed reference blocks to mitigate artifacts created duringscaling, quantization, and transform. Such artifacts could otherwisecause inaccurate prediction (and create additional artifacts) whensubsequent blocks are predicted.

The filter control analysis component 227 and the in-loop filterscomponent 225 apply the filters to the residual blocks and/or toreconstructed image blocks. For example, the transformed residual blockfrom the scaling and inverse transform component 229 may be combinedwith a corresponding prediction block from intra-picture predictioncomponent 217 and/or motion compensation component 219 to reconstructthe original image block. The filters may then be applied to thereconstructed image block. In some examples, the filters may instead beapplied to the residual blocks. As with other components in FIG. 2, thefilter control analysis component 227 and the in-loop filters component225 are highly integrated and may be implemented together, but aredepicted separately for conceptual purposes. Filters applied to thereconstructed reference blocks are applied to particular spatial regionsand include multiple parameters to adjust how such filters are applied.The filter control analysis component 227 analyzes the reconstructedreference blocks to determine where such filters should be applied andsets corresponding parameters. Such data is forwarded to the headerformatting and CABAC component 231 as filter control data for encoding.The in-loop filters component 225 applies such filters based on thefilter control data. The filters may include a deblocking filter, anoise suppression filter, a SAO filter, and an adaptive loop filter.Such filters may be applied in the spatial/pixel domain (e.g., on areconstructed pixel block) or in the frequency domain, depending on theexample.

When operating as an encoder, the filtered reconstructed image block,residual block, and/or prediction block are stored in the decodedpicture buffer component 223 for later use in motion estimation asdiscussed above. When operating as a decoder, the decoded picture buffercomponent 223 stores and forwards the reconstructed and filtered blockstoward a display as part of an output video signal. The decoded picturebuffer component 223 may be any memory device capable of storingprediction blocks, residual blocks, and/or reconstructed image blocks.

The header formatting and CABAC component 231 receives the data from thevarious components of codec system 200 and encodes such data into acoded bitstream for transmission toward a decoder. Specifically, theheader formatting and CABAC component 231 generates various headers toencode control data, such as general control data and filter controldata. Further, prediction data, including intra-prediction and motiondata, as well as residual data in the form of quantized transformcoefficient data are all encoded in the bitstream. The final bitstreamincludes all information desired by the decoder to reconstruct theoriginal partitioned video signal 201. Such information may also includeintra-prediction mode index tables (also referred to as code wordmapping tables), definitions of encoding contexts for various blocks,indications of most probable intra-prediction modes, an indication ofpartition information, etc. Such data may be encoded be employingentropy coding. For example, the information may be encoded by employingcontext adaptive variable length coding (CAVLC), CABAC, syntax-basedcontext-adaptive binary arithmetic coding (SBAC), probability intervalpartitioning entropy (PIPE) coding, or another entropy coding technique.Following the entropy coding, the coded bitstream may be transmitted toanother device (e.g., a video decoder) or archived for latertransmission or retrieval.

The present disclosure relates to modifications to down-samplingmechanisms to support intra-prediction to reduce resource usage withoutsignificantly reducing accuracy, and hence coding efficiency whencompressing blocks. For example, the present disclosure improves thefunctionality of intra-picture estimation component 215 and/orintra-picture prediction component 217. Specifically, the intra-pictureestimation component 215 and/or intra-picture prediction component 217obtain neighboring blocks of luma samples as part of predicting acurrent block of chroma samples. The intra-picture estimation component215 and/or intra-picture prediction component 217 may then down-samplethe luma samples from the neighboring blocks for use as referencesamples when performing cross-component intra-prediction. Further, theintra-picture estimation component 215 and/or intra-picture predictioncomponent 217 use a single column and/or row when down-sampling toreduce line buffer memory usage without significantly reducing accuracyof the intra-prediction process.

FIG. 3 is a block diagram illustrating an example video encoder 300 thatmay perform cross-component intra-prediction. Video encoder 300 may beemployed to implement the encoding functions of codec system 200 and/orimplement steps 101, 103, 105, 107, and/or 109 of operating method 100.Encoder 300 partitions an input video signal, resulting in a partitionedvideo signal 301, which is substantially similar to the partitionedvideo signal 201. The partitioned video signal 301 is then compressedand encoded into a bitstream by components of encoder 300.

Specifically, the partitioned video signal 301 is forwarded to anintra-picture prediction component 317 for intra-prediction. Theintra-picture prediction component 317 may be substantially similar tointra-picture estimation component 215 and intra-picture predictioncomponent 217. The partitioned video signal 301 is also forwarded to amotion compensation component 321 for inter-prediction based onreference blocks in a decoded picture buffer component 323. The motioncompensation component 321 may be substantially similar to motionestimation component 221 and motion compensation component 219. Theprediction blocks and residual blocks from the intra-picture predictioncomponent 317 and the motion compensation component 321 are forwarded toa transform and quantization component 313 for transformation andquantization of the residual blocks. The transform and quantizationcomponent 313 may be substantially similar to the transform scaling andquantization component 213. The transformed and quantized residualblocks and the corresponding prediction blocks (along with associatedcontrol data) are forwarded to an entropy coding component 331 forcoding into a bitstream. The entropy coding component 331 may besubstantially similar to the header formatting and CABAC component 231.

The transformed and quantized residual blocks and/or the correspondingprediction blocks are also forwarded from the transform and quantizationcomponent 313 to an inverse transform and quantization component 329 forreconstruction into reference blocks for use by the motion compensationcomponent 321. The inverse transform and quantization component 329 maybe substantially similar to the scaling and inverse transform component229. In-loop filters in an in-loop filters component 325 are alsoapplied to the residual blocks and/or reconstructed reference blocks,depending on the example. The in-loop filters component 325 may besubstantially similar to the filter control analysis component 227 andthe in-loop filters component 225. The in-loop filters component 325 mayinclude multiple filters as discussed with respect to in-loop filterscomponent 225. The filtered blocks are then stored in a decoded picturebuffer component 323 for use as reference blocks by the motioncompensation component 321. The decoded picture buffer component 323 maybe substantially similar to the decoded picture buffer component 223.

For example, the intra-picture prediction component 317 can beconfigured to perform cross-component intra-prediction. Incross-component intra-prediction, the chroma components for a currentblock are predicted based in part on the luma components of neighboringblocks. In an encoder 300, the neighboring blocks may be encoded andthen later reconstructed to act as reference blocks for further blocks.Hence, the chroma components of the current block are predicted based onreconstructed neighboring luma samples from reconstructed neighboringblocks. Multiple cross-component mechanisms are discussed in greaterdetail below. Regardless of the cross-component mechanisms used, theneighboring luma components are down-sampled. This is because lumablocks are generally at four times the resolution of chroma blocks, andhence contain four times the number of samples of the chroma blocks.Down-sampling allows the number of reference luma samples to match thenumber of chroma samples to provide for an accurate comparison whenperforming cross-component intra-prediction.

The intra-picture prediction component 317 performs down-sampling byemploying a single row and/or a single column of luma samples from theneighboring reference blocks. By way of comparison, employing multiplerows and columns of luma samples during down-sampling results indown-sampled luma reference samples that are not significantly differentthan the down-sampled luma reference samples from a single line/column.However, the down-sampled luma reference samples from multiplerows/lines employ significantly more line buffer memory space togenerate than the down-sampled luma reference samples from a singleline/row. Accordingly, by employing a single row/column of luma samplesfor down-sampling when determining neighboring luma reference samples,the amount of line buffer memory space is significantly reduced withoutsignificantly impacting the accuracy of the resulting down-sampled lumareference samples. As such, the intra-picture prediction component 317employs fewer memory resources without significantly reducing codingefficiency, which results in improved functionality of the intra-pictureprediction component 317.

FIG. 4 is a block diagram illustrating an example video decoder 400 thatmay perform cross-component intra-prediction. Video decoder 400 may beemployed to implement the decoding functions of codec system 200 and/orimplement steps 111, 113, 115, and/or 117 of operating method 100.Decoder 400 receives a bitstream, for example from an encoder 300, andgenerates a reconstructed output video signal based on the bitstream fordisplay to an end user.

The bitstream is received by an entropy decoding component 433. Theentropy decoding component 433 is configured to implement an entropydecoding scheme, such as CAVLC, CABAC, SBAC, PIPE coding, or otherentropy coding techniques. For example, the entropy decoding component433 may employ header information to provide a context to interpretadditional data encoded as code words in the bitstream. The decodedinformation includes any desired information to decode the video signal,such as general control data, filter control data, partitioninformation, motion data, prediction data, and quantized transformcoefficients from residual blocks. The quantized transform coefficientsare forwarded to an inverse transform and quantization component 429 forreconstruction into residual blocks. The inverse transform andquantization component 429 may be similar to inverse transform andquantization component 329.

The reconstructed residual blocks and/or prediction blocks are forwardedto intra-picture prediction component 417 for reconstruction into imageblocks based on intra-prediction operations. The intra-pictureprediction component 417 may be similar to intra-picture estimationcomponent 215 and an intra-picture prediction component 217.Specifically, the intra-picture prediction component 417 employsprediction modes to locate a reference block in the frame and applies aresidual block to the result to reconstruct intra-predicted imageblocks. The reconstructed intra-predicted image blocks and/or theresidual blocks and corresponding inter-prediction data are forwarded toa decoded picture buffer component 423 via an in-loop filters component425, which may be substantially similar to decoded picture buffercomponent 223 and in-loop filters component 225, respectively. Thein-loop filters component 425 filters the reconstructed image blocks,residual blocks, and/or prediction blocks, and such information isstored in the decoded picture buffer component 423. Reconstructed imageblocks from decoded picture buffer component 423 are forwarded to amotion compensation component 421 for inter-prediction. The motioncompensation component 421 may be substantially similar to motionestimation component 221 and/or motion compensation component 219.Specifically, the motion compensation component 421 employs motionvectors from a reference block to generate a prediction block andapplies a residual block to the result to reconstruct an image block.The resulting reconstructed blocks may also be forwarded via the in-loopfilters component 425 to the decoded picture buffer component 423. Thedecoded picture buffer component 423 continues to store additionalreconstructed image blocks, which can be reconstructed into frames viathe partition information. Such frames may also be placed in a sequence.The sequence is output toward a display as a reconstructed output videosignal.

As with encoder 300, the intra-picture prediction component 417 of thedecoder 400 can be configured to perform cross-componentintra-prediction. In cross-component intra-prediction, the chromacomponents for a chroma block are predicted based on luma components ofa corresponding reconstructed luma block block as well as based onparameters obtained from reconstructed neighboring chroma samples inneighboring chroma blocks and reconstructed neighboring luma samples inthe neighboring luma blocks. For example in a decoder 400, theneighboring luma and chroma blocks may be reconstructed and then used asreference blocks for further blocks (e.g., a current block). Hence, thechroma components of the chroma block are in part predicted based onreconstructed neighboring luma samples from reconstructed neighboringluma blocks and reconstructed neighboring chroma samples fromreconstructed neighboring chroma blocks. Multiple cross-componentmechanisms are discussed in greater detail below. Regardless of thecross-component mechanisms used, the neighboring luma components aredown-sampled. This is because luma blocks are generally at 4-times theresolution of chroma blocks, and hence contain 4-times the number ofsamples of the chroma blocks. Down-sampling allows the number ofreference luma samples to match the number of reference chroma samplesto provide for an accurate comparison when performing cross-componentintra-prediction.

The intra-picture prediction component 417 performs down-sampling byemploying a single row and/or a single column of luma samples from theneighboring reference luma blocks. By way of comparison, employingmultiple rows and columns of luma samples during down-sampling resultsin down-sampled neighboring luma reference samples that are notsignificantly different than the down-sampled neighboring luma referencesamples from a single line/column. However, the down-sampled lumareference samples from multiple rows/lines employ significantly moreline buffer memory space to generate than the down-sampled lumareference samples from a single line/row. Accordingly, by employing asingle row/column of neighboring luma samples for down-sampling, theamount of line buffer memory space is significantly reduced withoutsignificantly impacting the accuracy of the resulting down-sampled lumareference samples. As such, the intra-picture prediction component 417employs fewer memory resources without significantly reducing codingefficiency, which results in improved functionality of the intra-pictureprediction component 417.

FIG. 5 is a schematic diagram illustrating an example ofintra-prediction modes 500 as employed in video coding. For example,intra-prediction modes 500 may be employed by steps 105 and 113 ofmethod 100, intra-picture estimation component 215 and an intra-pictureprediction component 217 of codec system 200, intra-picture predictioncomponent 317 of encoder 300, and/or intra-picture prediction component417 of decoder 400.

Intra-prediction involves matching one or more samples in a currentblock in a CU to one or more reference samples of one or moreneighboring blocks. The current block can then be represented as aselected prediction mode index and a residual block, which is muchsmaller than representing all of the sample values contained in thecurrent block. Intra-prediction can be used when there is no availablereference frame, or when inter-predication coding is not used for thecurrent block, slice, and/or frame. The reference samples forintra-prediction are generally derived from neighboring blocks in thesame frame. Advanced Video Coding (AVC), also known as H.264, andH.265/HEVC both employ a reference line of boundary samples of adjacentblocks as reference samples for intra-prediction. In order to coverdifferent textures or structural characteristics many differentintra-prediction modes 500 are employed. H.265/HEVC supports a total ofthirty five single component intra-prediction modes 500 that spatiallycorrelate a current block of samples to one or more reference samples ofthe same type (e.g., luma samples predicted by reference luma samplesand chroma samples predicted by reference chroma samples). Specifically,intra-prediction modes 500 include thirty-three directional predictionmodes indexed as modes two through thirty four, a DC mode indexed asmode one, and a planar mode indexed as mode zero.

During encoding, the encoder matches the luma/chroma values of a currentblock in a CU with the luma/chroma values of corresponding referencesamples in a reference line across the edges of neighboring blocks. Whenthe best match is found with one of the reference lines, the encoderselects one of the directional intra-prediction modes 500 that points tothe best matching reference line (e.g., smallest difference in samplevalue(s)). For clarity of discussion, acronyms are employed below toreference particular directional intra-prediction modes 500. DirSdenotes the starting directional intra-prediction mode when countingclockwise from the bottom left (e.g., mode two in HEVC). DirE denotesthe ending directional intra-prediction mode when counting clockwisefrom the bottom left (e.g., mode thirty four in HEVC). DirD denotes themiddle directional intra-coding mode when counting clockwise from thebottom left (e.g., mode eighteen in HEVC). DirH denotes a horizontalintra-prediction mode (e.g., mode ten in HEVC). DirV denotes a verticalintra-prediction mode (e.g., mode twenty six in HEVC).

DC mode acts as a smoothing function and derives a prediction value of ablock in the CU as an average value of all the reference samples in thereference line traversing the neighboring blocks. Planar mode returns aprediction value that indicates a smooth transition (e.g., constantslope of values) between samples at the bottom and top left or top leftand top right of the reference line of reference samples.

For planar, DC, and prediction modes from DirH to DirV, the samples inboth the top row of the reference line and the left column of thereference line are used as reference samples. For prediction modes withprediction directions from DirS to DirH (including DirS and DirH), thereference samples in the neighboring blocks on the left column of thereference line are used as reference samples. For prediction modes withprediction directions from DirV to DirE (including DirV and DirE), thereference samples of the neighboring blocks on the top row of thereference line are used as reference samples. Accordingly,intra-prediction modes 500 can be used to indicate a spatial and/ordirectional relationship between samples and one or more referencesamples.

FIG. 6 is a schematic diagram illustrating an example mechanism ofperforming cross-component intra-prediction 600. Cross-componentintra-prediction 600 may be performed by an intra-picture estimationcomponent 215 and/or an intra-picture prediction component 217 of acodec system 200, an intra-picture prediction component 317 of anencoder 300, and/or an intra-picture prediction component 417 of adecoder 400. Specifically, cross-component intra-prediction 600 can beemployed during block compression at step 105 of method 100 and duringblock decoding at step 113 of method 100 at an encoder and a decoder,respectively. Cross-component intra-prediction 600 operates in a mannerthat is substantially similar to intra-prediction modes 500. However,cross-component intra-prediction 600 uses luma reference samples topredict chroma samples in order to reduce cross-component redundancy.

Cross-component intra-prediction 600 operates on a chroma block 601based on reference samples from a corresponding luma block 611 in thesame CU, neighboring chroma blocks 607, and neighboring luma blocks 617.Specifically, a CU contains a luma block and two chroma blocks. Thechroma block 601 contains chroma samples once reconstructed. The chromasamples may include red difference chroma (Cr) samples, blue differencechroma (Cb) samples, or combinations thereof. The neighboring chromablocks 607 contain neighboring chroma samples, and the neighboring lumablocks 617 contain neighboring luma samples. A neighboring chroma block607 is a block of chroma samples that is directly adjacent to the chromablock 601. A neighboring luma block 617 is a block of luma samples thatis directly adjacent to the luma block 611. The luma block 611 ispositioned in the same location as the chroma block 601, and arerendered together to express both light and color, respectively, in animage. Cross-component intra-prediction 600 operates based on thecorresponding luma samples from the luma block 611, the neighboringchroma reference samples 603 in the neighboring chroma blocks 607, andthe neighboring luma reference samples 613 in the neighboring lumablocks 617. Specifically, chroma samples in the current block 601 can bepredicted by a combination of luma samples in the luma block 611 in thesame CU as the current block as well as set(s) of luma samples andchroma samples acting as neighboring reference luma samples 613 andneighboring chroma reference samples 603 in the neighboring luma blocks607 and in the neighboring chroma blocks 607, respectively. Neighboringchroma reference samples 603 are taken from rows of the neighboringchroma blocks 607 that are directly adjacent to the chroma block 601.Neighboring chroma reference samples 603 are also taken from columns ofthe neighboring chroma blocks 607 that are directly adjacent to thechroma block 601. Neighboring luma reference samples 613 are taken fromrows of the neighboring luma blocks 617 that are directly adjacent tothe luma block 611. Neighboring luma reference samples 613 are alsotaken from columns of the neighboring luma blocks 617 that are directlyadjacent to the luma block 611.

Several mechanisms may be employed to predict chroma samples in thecurrent block 601 based on luma samples in the luma blocks 611 usingparameters generated based on the neighboring luma reference samples 613and neighboring chroma reference samples 603 in the neighboring lumablocks 617 and neighboring chroma blocks 607, respectively, as discussedin greater detail below. In general, a linear model is created todetermine parameters by correlating the chroma samples in the chromablock 601 to the luma samples in the luma block 611 in the same CU andneighboring luma reference samples 613 and neighboring chroma referencesamples 603. The model parameters may be calculated by minimizingregression error between the neighboring luma reference samples 613 andneighboring chroma reference samples 603. Another approach involvescalculating model parameters based on the minimum and maximum lumavalues from the neighboring luma reference samples 613. Such computationmechanisms are discussed in detail below.

FIG. 7 is a schematic diagram illustrating an example mechanism ofperforming CCLM intra-prediction 700. CCLM intra-prediction 700 is atype of cross-component intra-prediction 600. Hence, CCLMintra-prediction 700 may be performed by an intra-picture estimationcomponent 215 and/or an intra-picture prediction component 217 of acodec system 200, an intra-picture prediction component 317 of anencoder 300, and/or an intra-picture prediction component 417 of adecoder 400. Specifically, CCLM intra-prediction 700 can be employedduring block compression at step 105 of method 100 and during blockdecoding at step 113 of method 100 at an encoder and a decoder,respectively.

CCLM intra-prediction 700 predicts chroma samples 703 in a chroma block701. The chroma samples 703 appear at integer positions shown asintersecting lines. The prediction is based in part on neighboringreference samples, which are depicted as black circles. Unlike withintra-prediction modes 500, the chroma samples 703 are not predictedsolely based on the neighboring chroma reference samples 705, which aredenoted as reconstructed chroma samples (Rec′C). The chroma samples 703are also predicted based on luma reference samples 713 and neighboringluma reference samples 715. Specifically, a CU contains a luma block 711and two chroma blocks 701. A model is generated that correlates thechroma samples 703 and the luma reference samples 713 in the same CU.Linear coefficients for the model are determined by comparing theneighboring luma reference samples 715 to the neighboring chromareference samples 705.

The luma reference samples 713 are selected from the luma block 711 inthe same CU as the chroma block 701. The neighboring luma referencesamples 715 are selected from luma samples in neighboring blocksadjacent to the luma block 711. The neighboring luma reference samples715 are selected by applying a template 717 to the neighboring blockabove the luma block 711 and applying a template 716 to the neighboringblock to the left to the luma block 711. As the luma reference samples713 are reconstructed, the luma reference samples 713 are denoted asreconstructed luma samples (Rec′L). The neighboring chroma referencesamples 705 are selected from chroma samples in neighboring blocksadjacent to the chroma block 701. The neighboring chroma referencesamples 705 are selected by applying a template 707 corresponding totemplate 717 to the neighboring chroma samples in the neighboring chromablock above the chroma block 701 and applying a template 706corresponding to template 716 to the neighboring chroma samples in theneighboring chroma block to the left to the chroma block 701. As theneighboring chroma reference samples 705 are reconstructed, theneighboring chroma reference samples 705 are denoted as reconstructedchroma samples (Rec′C). Also, as used herein, a template 706, 707, 716,and 717 is a mechanism that correlates neighboring luma referencesamples 715 to neighboring chroma reference samples 705.

As shown, the luma block 711 contains four times the samples as thechroma block 701. Specifically, the chroma block 701 contains N numberof samples by N number of samples while the luma block 711 contains 2Nnumber of samples by 2N number of samples. Hence, the luma block 711 isfour times the resolution of the chroma block 701. For the prediction tooperate on the luma reference samples 713 and the neighboring lumareference samples 715, the luma reference samples 713 and theneighboring luma reference samples 715 are down-sampled to provide anaccurate comparison with the neighboring chroma reference samples 705and the chroma samples 703. Down-sampling is the process of reducing theresolution of a group of sample values. For example, when YUV4:2:0format is used, the luma samples may be down-sampled by a factor of four(e.g., width by two, and height by two). YUV is a color encoding systemthat employs a color space in terms of luma components Y and twochrominance components U and V.

Once the neighboring luma reference samples 715 and the luma referencesamples 713 are down-sampled, a model can be generated to predict thechroma samples 703 of the chroma block 701. Specifically, in CCLMintra-prediction 700, a prediction for chroma samples 703 of the chromablock 701 can be determined according to the model described by equation1:

pred_(C)(i,j)=α·rec_(L)′(i,j)+β  (1)

where pred_(C)(i,j) are the prediction chroma samples 703 of chromablock 701 at a height i and a width j, rec_(L)′(i,j) are thereconstructed down-sampled luma reference samples 713 and α and β arelinear coefficients determined by comparing the neighboring down-sampledluma reference samples 715 and the chroma reference samples 705.

In one example, α and β are determined by minimizing the regressionerror between the down-sampled neighboring luma reference samples 715and the chroma reference samples 705. This can be done according toequations 2 and 3:

$\begin{matrix}{\alpha = \frac{{N \cdot {\Sigma\left( {{L(n)} \cdot {C(n)}} \right)}} - {\Sigma\;{{L(n)} \cdot \Sigma}\;{C(n)}}}{{N \cdot {\Sigma\left( {{L(n)} \cdot {L(n)}} \right)}} - {\Sigma\;{{L(n)} \cdot \Sigma}\;{L(n)}}}} & (2) \\{\beta = \frac{{\Sigma\;{C(n)}} - {{\alpha \cdot \Sigma}\;{L(n)}}}{N}} & (3)\end{matrix}$

where L(n) represents the down-sampled top and left neighboringreconstructed luma samples (e.g., down-sampled neighboring lumareference samples 715), C(n) represents the top and left neighboringreconstructed chroma samples (e.g., the neighboring chroma referencesamples 705), and value of N is equal to the sum of the width and heightof the current chroma coding block (e.g., chroma block 701). In anotherexample, α and β are determined based on the minimum and maximum valueof the down-sampled neighboring luma reference samples 715 as discussedwith respect to FIG. 8 below.

As noted above, the neighboring luma reference samples 715 and the lumareference samples 713 are down-sampled prior to generating the linearmodel. Further, employing multiple lines and columns to generate theneighboring luma reference samples 715 does not significantly increasethe accuracy of the remaining calculations pursuant to CCLMintra-prediction 700. As such, a single row and/or column of neighboringluma reference samples 715 can be employed during down-sampling, whichreduces utilization of the line buffer memory without significantlyimpacting the accuracy and/or coding efficiency of CCLM intra-prediction700.

FIG. 8 is a graph illustrating an example mechanism 800 of determininglinear model parameters to support CCLM intra-prediction 700. Inmechanism 800, α and β, as used in equation 1, are determined based onthe minimum and maximum value of the down-sampled neighboring lumareference samples. This is an alternate approach to determining α and βbased on minimizing the regression error.

Neighboring luma reference values can be compared to correspondingneighboring chroma reference values on a graph as shown. A line can bedrawn through the point containing the minimum neighboring lumareference value and the maximum neighboring luma reference value. Such aline can be characterized as Y=α·X+β. The slope α and the Y intercept βcan be determined based on two points according to equations 4 and 5.

$\begin{matrix}{\alpha = \frac{y_{B} - y_{A}}{x_{B} - x_{A}}} & (4) \\{\beta = {y_{A} - {\alpha\; x_{A}}}} & (5)\end{matrix}$

where (x_(A), y_(A)) is a coordinate defined by the minimum neighboringluma reference value and a corresponding chroma reference value and(x_(B), y_(B)) is a coordinate defined by the maximum neighboring lumareference value and a corresponding chroma reference value. Hence, α andβ can be determined based on a line passing through the minimum andmaximum value of the down-sampled neighboring luma reference samples.The α and β can then be used in equation 1 to determine the predictionvalues for the chroma samples in the current block.

FIGS. 9-10 are schematic diagrams illustrating an example mechanism ofperforming MDLM intra-prediction. MDLM intra-prediction operates in amanner similar to CCLM intra-prediction 700, but employs differenttemplates. Specifically, MDLM intra-prediction uses both across-component linear model prediction (CCIP)_A mode 900 and a CCIP_Lmode 1000 when determining linear model coefficients α and β. Forexample, MDLM intra-prediction may calculate linear model coefficients αand β using CCIP_A mode 900 and CCIP_L mode 1000. MDLM intra-predictionmay then select CCIP_A mode 900 or CCIP_L mode 1000 depending on theresult that provides the greatest coding efficiency (e.g., the leastresidual samples). In another example, MDLM intra-prediction may useboth CCIP_A mode 900 or CCIP_L mode 1000 to determine linear modelcoefficients α and β.

As such, MDLM intra-prediction using CCIP_A mode 900 or CCIP_L mode 1000is a type of cross-component intra-prediction 600. Accordingly, MDLMintra-prediction using CCIP_A mode 900 or CCIP_L mode 1000 may beperformed by an intra-picture estimation component 215 and/or anintra-picture prediction component 217 of a codec system 200, anintra-picture prediction component 317 of an encoder 300, and/or anintra-picture prediction component 417 of a decoder 400. Specifically,MDLM intra-prediction using CCIP_A mode 900 or CCIP_L mode 1000 can beemployed during block compression at step 105 of method 100 and duringblock decoding at step 113 of method 100 at an encoder and a decoder,respectively.

CCIP_A mode 900 generates a model to predict chroma samples 903 in achroma block 901 based on luma reference samples 913 in a luma block911, where the luma block 911 is in the same CU as the chroma block 901,in a manner similar to CCLM intra-prediction 700. Specifically, a linearmodel is generated according to equation 1 above. Further, a template917 and a corresponding template 907 are employed to select neighboringluma reference samples 915 and neighboring chroma reference samples 905in a manner similar to CCLM intra-prediction 700. The difference is thatthe templates 907 and 917 are shaped differently. As with CCLMintra-prediction 700, CCIP_A mode 900 down-samples the neighboring lumareference samples 915 and the luma reference samples 913. CCIP_A mode900 uses the luma reference samples 913 to determine Rec′L inequation 1. CCIP_A mode 900 then uses down-sampled neighboring lumareference samples 915 and neighboring chroma reference samples 905 todetermine linear model coefficients α and β. The linear modelcoefficients α and β can then be employed to complete the linear modelaccording to equation 1 to obtain the prediction for the chroma samples903.

The templates 907 and 917 are applied to neighboring chroma blocks andluma blocks, respectively, that are above and directly adjacent to thechroma block 901 and the corresponding luma block 911, respectively. Thetemplates 907 and 917 do not obtain samples to the left to the chromablock 901 and the corresponding luma block 911. As templates 907 and 917are only applied above the chroma block 901 and the luma block 911, thetemplates 907 and 917 are extended horizontally past the chroma block901 and the corresponding luma block 911, respectively, to obtain moresamples. This may allow templates 907 and 917 to obtain an equivalentnumber of neighboring chroma reference samples 905 and neighboring lumareference samples 915, respectively, to the numbers used by the CCLMintra-prediction 700 when determining linear model coefficients α and β.

CCIP_L mode 1000 generates a model to predict chroma samples 1003 in achroma block 1001 based on luma reference samples 1013 in a luma block1011, where the luma block 1011 is in the same CU as the chroma block1001, in a manner similar to CCLM intra-prediction 700. Specifically, alinear model is generated according to equation 1 above. Further, atemplate 1016 and a corresponding template 1006 are employed to selectneighboring luma reference samples 1015 and neighboring chroma referencesamples 1005 in a manner similar to CCLM intra-prediction 700. Thedifference is that the templates 1006 and 1016 are shaped differently.As with CCLM intra-prediction 700, CCIP_L mode 1000 down-samples theneighboring luma reference samples 1015 and the luma reference samples1013. CCIP_A mode 1000 uses the luma reference samples 1013 to determineRec′L in equation 1. CCIP_A mode 1000 then uses down-sampled neighboringluma reference samples 1015 and neighboring chroma reference samples1005 to determine linear model coefficients α and β. The linear modelcoefficients α and β can then be employed to complete the linear modelaccording to equation 1 to obtain the prediction for the chroma samples1003.

The templates 1006 and 1016 are applied to neighboring chroma blocks andluma blocks, respectively, that are to the left to and directly adjacentto the chroma block 1001 and the corresponding luma block 1011,respectively. The templates 1006 and 1016 do not obtain samples abovethe chroma block 1001 and the corresponding luma block 1011. Astemplates 1006 and 1016 are only applied to the left to the chroma block1001 and the luma block 1011, the templates 1006 and 1016 are extendedvertically below the chroma block 1001 and the corresponding luma block1011, respectively, to obtain more samples. This may allow templates1006 and 1016 to obtain an equivalent number of neighboring chromareference samples 1005 and neighboring luma reference samples 1015,respectively, to the numbers used by the CCLM intra-prediction 700 whendetermining linear model coefficients α and β.

As noted above, the neighboring luma reference samples 915 and 1015 andthe luma reference samples 913 and 1013 are down-sampled prior togenerating the linear model. Further, employing multiple lines andcolumns to generate the neighboring luma reference samples 915 and 1015does not significantly increase the accuracy of the remainingcalculations pursuant to MDLM intra-prediction using CCIP_A mode 900and/or CCIP_L mode 1000. As such, a single row and/or column ofneighboring luma reference samples 915 and 1015 can be employed duringdown-sampling, which reduces utilization of the line buffer memorywithout significantly impacting the accuracy and/or coding efficiency ofMDLM intra-prediction.

FIG. 11 is a graph 1100 illustrating an example mechanism of determininglinear model parameters to support MMLM intra-prediction. MMLMintra-prediction, as shown in graph 1100 is a type of cross-componentintra-prediction 600. Hence, MMLM intra-prediction may be performed byan intra-picture estimation component 215 and/or an intra-pictureprediction component 217 of a codec system 200, an intra-pictureprediction component 317 of an encoder 300, and/or an intra-pictureprediction component 417 of a decoder 400. Specifically, MMLMintra-prediction can be employed during block compression at step 105 ofmethod 100 and during block decoding at step 113 of method 100 at anencoder and a decoder, respectively.

MMLM intra-prediction is similar to CCLM intra-prediction 700. Thedifference is that in MMLM, the neighboring chroma reference samples705, the neighboring luma reference samples 715, and the luma referencesamples 713 are placed into groups by comparing the relevant luma value(e.g., Rec′L) to a threshold. CCLM intra-prediction 700 is thenperformed on each group to determine linear model coefficients α and βand complete a corresponding linear model according to equation 1. Theprediction for each group may be determined according to equation sixbelow:

$\begin{matrix}\left\{ \begin{matrix}{{{Pred}_{C}\left\lbrack {x,y} \right\rbrack} = {{\alpha_{1} \times {{Rec}_{L}^{\prime}\left\lbrack {x,y} \right\rbrack}} + \beta_{1}}} & {{{if}\mspace{14mu}{{Rec}_{L}^{\prime}\left\lbrack {x,y} \right\rbrack}} \leq {Threshold}} \\{{{Pred}_{C}\left\lbrack {x,y} \right\rbrack} = {{\alpha_{2} \times {{Rec}_{L}^{\prime}\left\lbrack {x,y} \right\rbrack}} + \beta_{2}}} & {{{if}\mspace{14mu}{{Rec}_{L}^{\prime}\left\lbrack {x,y} \right\rbrack}} > {Threshold}}\end{matrix} \right. & (6)\end{matrix}$

where the variables of equation 6 is defined similarly to equation 1with a subscript of one indicating relation to a first group and asubscript of two indicating a relationship to a second group.

As shown by graph 1100, linear model coefficients α₁ and β₁ can becalculated for a first group and linear model coefficients α₂ and β₂ canbe calculated for a second group. As a specific example, such values maybe an α₁ of two, a β₁ of one, an α₂ of one half, and a β₂ of negativeone where the threshold is a luma value of seventeen. The MMLMintra-prediction can then select the resulting model that provides theleast residual samples and/or results in the greatest coding efficiency.

As with the other cross component intra-prediction modes discussedherein, the neighboring luma reference samples and the luma referencesamples are down-sampled prior to generating the linear model. Further,employing multiple lines and columns to generate the neighboring lumareference samples does not significantly increase the accuracy of theremaining calculations pursuant to MMLM intra-prediction. As such, asingle row and/or column of neighboring luma reference samples can beemployed during down-sampling, which reduces utilization of the linebuffer memory without significantly impacting the accuracy and/or codingefficiency of MMLM intra-prediction.

It should be noted that the encoder may select the intra-prediction modeused (e.g., CCLM, MDLM, and/or MMLM) as well as select the relevantmodel to use (e.g., CCIP_A, CCIP_L, group one, group two, etc.) as partof the corresponding intra-prediction mode. Such information can besignaled to the decoder in syntax, for example by employing flags. Thedecoder can then use the indicated intra-prediction mode to reconstructthe chroma samples for a chroma block.

FIGS. 12-15 are schematic diagrams illustrating example mechanisms 1200,1300, 1400, and 1500 of down-sampling to support cross-componentintra-prediction, for example according to cross-componentintra-prediction 600, CCLM intra-prediction 700, mechanism 800, MDLMintra-prediction using CCIP_A mode 900 and CCIP_L mode 1000, and/or MMLMintra-prediction as depicted in graph 1100. Hence, mechanisms 1200,1300, and 1400 can be may be performed by an intra-picture estimationcomponent 215 and/or an intra-picture prediction component 217 of acodec system 200, an intra-picture prediction component 317 of anencoder 300, and/or an intra-picture prediction component 417 of adecoder 400. Specifically, mechanisms 1200, 1300, 1400, and 1500 can beemployed during block compression at step 105 of method 100 and duringblock decoding at step 113 of method 100 at an encoder and a decoder,respectively.

Mechanism 1200 down-samples two rows 1218 and 1219 of neighboring lumareference samples and three columns 1220, 1221, and 1222 of neighboringluma reference samples. The rows 1218 and 1219 and columns 1220, 1221,and 1222 are directly adjacent to a luma block 1211 that shares a CUwith a chroma block being predicted according to cross-componentintra-prediction. After down-sampling, the rows 1218 and 1219 ofneighboring luma reference samples become a single row 1216 ofdown-sampled neighboring luma reference samples. Further, the columns1220, 1221, and 1222 of neighboring luma reference samples aredown-sampled resulting in a single column 1217 of down-sampledneighboring luma reference samples. In addition, the luma samples of theluma block 1211 are down-sampled to create down-sampled luma referencesamples 1212. The down-sampled luma reference samples 1212 and thedown-sampled neighboring luma reference samples from the row 1216 andthe column 1217 can then be employed for cross-componentintra-prediction according to equation 1. It should be noted that thedimensions of rows 1218 and 1219 and columns 1220, 1221, and 1222 mayextend beyond the luma block 1211 as shown in FIG. 12. For example, thenumber of top neighboring luma reference samples in each row 1218/1219,which may be denoted as M, is larger than the number of luma samples ina row of the luma block 1211, which may be denoted as W. Further, thenumber of left neighboring luma reference samples in each column1220/1221/1222, which may be denoted as N, is larger than the number ofluma samples in a column of the luma block 1211, which may be denoted asH.

In an example, mechanism 1200 may be implemented as follows. For a lumablock 1211, the two top neighboring rows 1218 and 1219, denoted as A1and A2, are used for down-sampling to get down-sampled neighboring row1216 denoted as A. A[i] is the ith sample in A, A1[i] is the ith samplein A1, and A2[i] is the ith sample in A2. In a specific example, a sixtap down-sampling filter can be applied to neighboring rows 1218 and1219 to obtain the down-sampled neighboring row 1216 according toequation 7.

A[i]=(A2[2i]*2+A2[2i−1]+A2[2i+1]+A1[2i]*2+A1[2i−1]+A1[2i+1]+4)>>3;  (7)

Further, the left neighboring columns 1220, 1221, and 1222 are denotedas L1, L2, and L3 and are used for down-sampling to obtain adown-sampled neighboring column 1217 denoted as L. L[i] is the ithsample in L, L1[i] is the ith sample in L1, L2[i] is the ith sample inL2, and L3[i] is the ith sample in L3. In an specific example, a six tapdown-sampling filter can be applied to neighboring columns 1220, 1221,and 1222 to obtain down-sampled neighboring column 1217 according toequation 8.

L[i]=(L2[2i]*2+L1[2i]+L3[2i]+L2[2i+1]*2+L1[2i+1]+L3[2i+1]+4)>>3;  (8)

Mechanism 1300 is substantially similar to mechanism 1200. Mechanism1300 includes a luma block 1311 with neighboring rows 1318 and 1319 andcolumns 1320, 1321, and 1322 of neighboring luma reference samples,which are similar to luma block 1211, rows 1218 and 1219, and columns1220, 1221, and 1222, respectively. The difference is that rows 1318 and1319 and columns 1320, 1321, and 1322 do not extend past the luma block1211. As in mechanism 1200, the luma block 1311, rows 1318 and 1319 andcolumns 1320, 1321, and 1322 are down-sampled to create down-sampledluma reference samples 1312, column 1317, and row 1316 containingdown-sampled neighboring luma reference samples. Column 1317 and row1316 do not extend beyond the block of down-sampled luma referencesamples 1312. Otherwise, down-sampled luma reference samples 1312,column 1317, and row 1316 are substantially similar to down-sampled lumareference samples 1212, column 1217, and row 1216, respectively.

Mechanism 1400 is similar to mechanisms 1200 and 1300 but employs asingle row 1218 of neighboring luma reference samples instead of tworows. Mechanism 1400 also employs three columns 1420, 1421, and 1422 ofneighboring luma reference samples. The row 1418 and columns 1420, 1421,and 1422 are directly adjacent to a luma block 1411 that shares a CUwith a chroma block being predicted according to cross-componentintra-prediction. After down-sampling, the row 1418 of neighboring lumareference samples becomes a row 1416 of down-sampled neighboring lumareference samples. Further, the columns 1420, 1421, and 1422 ofneighboring luma reference samples are down-sampled resulting in asingle column 1417 of down-sampled neighboring luma reference samples.Further, the luma samples of the luma block 1411 are down-sampled tocreate down-sampled luma reference samples 1412. The down-sampled lumareference samples 1412 and the down-sampled neighboring luma referencesamples from the row 1416 and the column 1417 can then be employed forcross-component intra-prediction according to equation 1.

During down-sampling, the rows and columns are stored in memory in aline buffer. By, omitting row 1319 during down-sampling and insteadusing a single row 1418 of values significantly decreases memory usagein the line buffer. However, the down-sampled neighboring luma referencesamples from the row 1316 have been found to be substantially similar tothe down-sampled neighboring luma reference samples from the row 1416.As such, omitting row 1319 during down-sampling and instead using asingle row 1418 results in reduced memory utilization in the linebuffer, and hence better processing speed, greater parallelism, fewermemory requirements, etc., without sacrificing accuracy and hence codingefficiency. Accordingly, in one example embodiment, a single row 1418 ofneighboring luma reference samples are down-sampled for use incross-component intra-prediction.

In an example, mechanism 1400 may be implemented as follows. For a lumablock 1411, the top neighboring row 1418, denoted as A1, is used fordown-sampling to get down-sampled neighboring row 1416 denoted as A.A[i] is the ith sample in A and A1 [i] is the ith sample in A1. In anspecific example, a three tap down-sampling filter can be applied toneighboring row 1418 to obtain the down-sampled neighboring row 1416according to equation 9.

A[i]=(A1[2i]*2+A1[2i−1]+A1[2i+1]+2)>>2;  (9)

Further, the left neighboring columns 1420, 1421, and 1422 are denotedas L1, L2, and L3 and are used for down-sampling to obtain adown-sampled neighboring column 1417 denoted as L. L[i] is the ithsample in L, L1[i] is the ith sample in L1, L2[i] is the ith sample inL2, and L3[i] is the ith sample in L3. In a specific example, a six tapdown-sampling filter can be applied to neighboring columns 1320, 1321,and 1322 to obtain down-sampled neighboring column 1317 according toequation 10.

L[i]=(L2[2i]*2+L1[2i]+L3[2i]+L2[2i+1]*2+L1[2i+1]+L0[2i+1]+4)>>3;   (10)

It should be noted that the mechanism 1400 is not limited to thedown-sampling filters described. For example, instead of employing athree tap down-sampling filter as described in equation 9, the samplescan also be fetched directly as in equation 11 below.

A[i]=A1[2i];  (11)

Mechanism 1500 is similar to mechanism 1300 but employs a single row1518 of neighboring luma reference samples and a single column 1520 ofneighboring luma reference samples instead of two rows 1318 and 1319 andthree columns 1320, 1321, and 1322, respectively. The row 1518 andcolumn 1520 are directly adjacent to a luma block 1511 that shares a CUwith a chroma block being predicted according to cross-componentintra-prediction. After down-sampling, the row 1518 of neighboring lumareference samples becomes a row 1516 of down-sampled neighboring lumareference samples. Further, the column 1520 of neighboring lumareference samples are down-sampled resulting in a single column 1517 ofdown-sampled neighboring luma reference samples. The down-sampledneighboring luma reference samples from the row 1516 and the column 1517can then be employed for cross-component intra-prediction according toequation 1.

Mechanism 1500 omits row 1319 and columns 1321 and 1322 duringdown-sampling and instead using a single row 1518 and single column 1520of values, which significantly decreases memory usage in the linebuffer. However, the down-sampled neighboring luma reference samplesfrom the row 1316 and column 1317 have been found to be substantiallysimilar to the down-sampled neighboring luma reference samples from therow 1516 and column 1517, respectively. As such, omitting row 1319 andcolumns 1321 and 1322 during down-sampling and instead using a singlerow 1518 and column 1520 results in reduced memory utilization in theline buffer, and hence better processing speed, greater parallelism,fewer memory requirements, etc., without sacrificing accuracy and hencecoding efficiency. Accordingly, in another example embodiment, a singlerow 1518 of neighboring luma reference samples and a single column 1520of neighboring luma reference samples are down-sampled for use incross-component intra-prediction.

In an example, mechanism 1500 may be implemented as follows. For a lumablock 1511, the top neighboring row 1518, denoted as A1, is used fordown-sampling to get down-sampled neighboring row 1516 denoted as A.A[i] is the ith sample in A and A1[i] is the ith sample in A1. In aspecific example, a three tap down-sampling filter can be applied toneighboring row 1518 to obtain the down-sampled neighboring row 1516according to equation 12.

A[i]=(A1[2i]*2+A1[2i−1]+A1[2i+1]+2)>>2;  (12)

Further, the left neighboring column 1520 is denoted as L1 is used fordown-sampling to obtain a down-sampled neighboring column 1517 denotedas L. L[i] is the ith sample in L and L1[i] is the ith sample in L1. Ina specific example, a two tap down-sampling filter can be applied toneighboring column 1520 to obtain down-sampled neighboring column 1517according to equation 13.

L[i]=(L1[2i]+L1[2i+1]+1)>>2;  (13)

In an alternate example, mechanism 1500 could be modified to employ anL2 column (e.g., column 1321) instead of an L1 column (e.g., column1520) when down-sampling. In such a case, a two tap down-sampling filtercan be applied to neighboring column L2 to obtain down-sampledneighboring column 1517 according to equation 14. It should be notedthat the mechanism 1500 is not limited to the down-sampling filtersdescribed. For example, instead of employing a two tap and a three tapdown-sampling filter as described in equations 12 and 13, the samplescan also be fetched directly as in equations 14 and 15 below.

A[i]=A1[2i];  (14)

L[i]=L2[2i];  (15)

Further, it should also be noted that mechanisms 1400 and 1500 can alsobe applied when the dimensions of rows 1418, 1416, 1518, 1516 and/orcolumns 1420, 1421, 1422, 1417, 1520, and/or 1517 extend beyond thecorresponding luma block 1411 and/or 1511 (e.g., as shown in FIG. 12).

FIG. 16 is a flowchart of an example method 1600 for cross-componentprediction of a block of video data. At step 1601, a reconstructed lumablock is down-sampled to obtain a down-sampled luma block. Thereconstructed luma block corresponds to a chroma block. At step 1603,first down-sampled samples of reconstructed top neighboring luma samplesthat are above the reconstructed luma block and/or second down-sampledsamples of reconstructed left neighboring luma samples that are left tothe reconstructed luma block are obtained. The reconstructed topneighboring luma samples are within a single row being adjacent to thereconstructed luma block. At step 1605, parameters of a LM are derivedbased on the first and/or second down-sampled samples, and reconstructedneighboring chroma samples that are above the chroma block and/orreconstructed neighboring chroma samples that are left to the chromablock. At step 1607, predicted chroma values of the chroma block aregenerated based on the parameters of the LM and the down-sampled lumablock.

Specifically, in the case of MDLM intra-prediction using CCIP_A mode900, the parameters of a LM are derived based on the first down-sampledsamples and reconstructed neighboring chroma samples that are above thechroma block. In the case of MDLM intra-prediction using CCIP_L mode1000, the parameters of a LM are derived based on the seconddown-sampled samples and reconstructed neighboring chroma samples thatare left to the chroma block. In the case of CCLM intra-prediction, theparameters of a LM are derived based on the first and seconddown-sampled samples, and reconstructed neighboring chroma samples thatare above the chroma block and reconstructed neighboring chroma samplesthat are left to the chroma block.

It should be noted that the reconstructed neighboring luma samples leftto the reconstructed luma block may include N columns of luma sampleswhich are left to the reconstructed luma block, wherein 0<N<=3 and N isa positive integer. Further, the reconstructed neighboring luma samplesleft to the reconstructed luma block may include a single column of lumasamples which are left to the reconstructed luma block. In addition, theLM may comprise one or more of: CCLM mode, MDLM mode, and MMLM mode.

FIG. 17 is a flowchart of another example method for cross-componentprediction of a block of video data. At step 1701, a reconstructed lumablock is down-sampled to obtain a down-sampled luma block. Thereconstructed luma block corresponds to a chroma block. At step 1703, amax luma value and a min luma value are determined based on firstdown-sampled samples of reconstructed top neighboring luma samples thatare above the reconstructed luma block and/or second down-sampledsamples of reconstructed left neighboring luma samples that are left tothe reconstructed luma block, wherein the reconstructed top neighboringluma samples are within a single row being adjacent to the reconstructedluma block. At step 1705, a first chroma value and a second chroma aredetermined based on reconstructed neighboring chroma samples of thechroma block, wherein the first chroma value and the second chroma valueare respectively associated with the max luma value and min luma value.At step 1707, parameters of a LM are derived based on the max luma valueand the min luma value and the first chroma value and the second chromavalue. At step 1709, predicted chroma values of the chroma block aregenerated based on the parameters of the LM and the down-sampled lumablock.

Specifically, in the case of MDLM intra-prediction using CCIP_A mode900, a max luma value and a min luma value are determined based on thefirst down-sampled samples of reconstructed top neighboring luma samplesthat are above the reconstructed luma block. In the case of MDLMintra-prediction using CCIP_L mode 1000, a max luma value and a min lumavalue are determined based on second down-sampled samples ofreconstructed left neighboring luma samples that are left to thereconstructed luma block. In the case of CCLM intra-prediction, a maxluma value and a min luma value are determined based on firstdown-sampled samples of reconstructed top neighboring luma samples thatare above the reconstructed luma block and second down-sampled samplesof reconstructed left neighboring luma samples that are left to thereconstructed luma block.

It should be noted that the reconstructed neighboring luma samples leftto the reconstructed luma block may include N columns of luma sampleswhich are left to the reconstructed luma block, wherein 0<N<=3 and N isa positive integer. Further, the reconstructed neighboring luma samplesleft to the reconstructed luma block may include a single column of lumasamples which are left to the reconstructed luma block. In addition, theLM may comprise one or more of: CCLM mode, MDLM mode, and MMLM mode.

For example, method 1600 may employ mechanism 1300 and/or 1400 as partof cross-component intra-prediction 600, CCLM intra-prediction 700,mechanism 800, MDLM intra-prediction using CCIP_A mode 900 and CCIP_Lmode 1000, and/or MMLM intra-prediction as depicted in graph 1100.Further, method 1600 can be may be performed by an intra-pictureestimation component 215 and/or an intra-picture prediction component217 of a codec system 200 as well as an intra-picture predictioncomponent 317 of an encoder 300. Specifically, method 1600 can beemployed during block compression at step 105 of method 100 at anencoder.

Method 1600 occurs during block compression, for example as part of arate distortion optimization process a video signal is received at theencoder. The video signal can be partitioned into a CU containing achroma block containing chroma samples and a corresponding luma blockcontaining luma samples acting as luma reference samples. The method1600 can determine to perform cross-component intra-prediction tocompress the chroma block of chroma samples.

The down-sampling includes down-sampling a single row of neighboringluma reference samples and/or down-sampling a single column ofneighboring luma reference samples.

The cross-component intra-prediction mechanisms employed to encode thechroma samples can include CCLM prediction mode intra-prediction, MDLMprediction mode intra-prediction, and/or MMLM prediction modeintra-prediction.

Linear model coefficients, denoted as α and β, are determined based onthe down-sampled neighboring luma samples and corresponding neighboringchroma samples. As discussed above, the linear model coefficients can bedetermined by minimizing the regression error between the down-sampledneighboring luma samples and the neighboring chroma samples by employingequations 2 and 3 as discussed hereinabove. In another example, thelinear model coefficients can be determined by computing a slope and a Yintercept of a line traversing the minimum and maximum value of thedown-sampled neighboring luma reference samples according to equations 4and 5 as discussed hereinabove.

Prediction information is determined for the chroma samples in thechroma block based on the linear model coefficients. Specifically, theprediction information for the chroma samples can be determinedaccording to equation 1. Hence, such prediction information can bedetermined based on the values of the down-sampled luma block (such as aluma block′) and based on the linear model coefficients α and β. Oncethe prediction information is determined, a residual block for thechroma block can be determined based on a difference between theprediction information and the chroma samples.

The residual data for the chroma block are encoded into a bitstream. Asnoted above, the prediction information for the chroma samples isdetermined via intra-prediction based on down-sampled neighboring lumasamples. Further, the down-sampled neighboring luma samples aregenerated from a single row of luma samples from the first neighboringblock and/or from a single column of luma samples from the secondneighboring block. Such encoding includes encoding an indication of anintra-prediction mode (e.g., CCLM, MDLM, and/or MMLM and/orcorresponding models/groups) and the residual block in the bitstream torepresent the chroma samples.

The bitstream is transmitted toward a decoder. The bitstream includesthe prediction information for the chroma samples to support decodingand display of the chroma samples as part of a video stream.

For example, method 1700 may employ mechanism 1300 and/or 1400 as partof cross-component intra-prediction 600, CCLM intra-prediction 700,mechanism 800, MDLM intra-prediction using CCIP_A mode 900 and CCIP_Lmode 1000, and/or MMLM intra-prediction as depicted in graph 1100.Further, method 1700 can be may be performed by an intra-pictureestimation component 215 and/or an intra-picture prediction component217 of a codec system 200 as well as an intra-picture predictioncomponent 417 of a decoder 400. Specifically, method 1700 can beemployed during block decoding at step 113 of method 100 at a decoder.

Method 1700 occurs during block decoding, for example as part ofreconstructing blocks from a bitstream for display. A bitstream isreceived. The bistream includes residual data for a chroma block. Themethod 1700 can determine to perform cross-component intra-prediction tocompress the chroma block of chroma samples.

The down-sampling includes down-sampling a single row of neighboringluma reference samples and/or down-sampling a single column ofneighboring luma reference samples.

The cross-component intra-prediction mechanism can be indicated bysyntax, flags, or other data in the bitstream and can include CCLMprediction mode intra-prediction, MDLM prediction mode intra-prediction,and/or MMLM prediction mode intra-prediction.

Linear model coefficients, denoted as α and β, are determined based onthe down-sampled neighboring luma samples and corresponding neighboringchroma samples. As discussed above, the linear model coefficients can bedetermined by minimizing the regression error between the down-sampledneighboring luma samples and the neighboring chroma samples by employingequations 2 and 3 as discussed hereinabove. In another example, thelinear model coefficients can be determined by computing a slope and a Yintercept of a line traversing the minimum and maximum value of thedown-sampled neighboring luma reference samples according to equations 4and 5 as discussed hereinabove.

Prediction information is determined for chroma samples in the chromablock based on the linear model coefficients. Specifically, theprediction information for the chroma samples can be determinedaccording to equation 1. Hence, such prediction information can bedetermined based on the values of the down-sampled luma referencesamples in the luma block from the same CU as the chroma block and basedon the linear model coefficients α and β determined at step 1706. Oncethe prediction information is determined, a residual block can bedetermined for the chroma block from the bitstream. It should be notedthat the preceding items may include determining an indication of anintra-prediction mode (e.g., CCLM, MDLM, and/or MMLM and/orcorresponding models/groups) and the residual block from the bitstream.

The chroma samples for the chroma block are decoded based on theprediction information, which is in turn determined via intra-predictionas indicated by the bitstream and based on the down-sampled neighboringluma samples. As noted above, the down-sampled neighboring luma samplesare generated from a single row of neighboring luma samples and/or froma single column of neighboring luma samples. Such decoding can includedecoding the chroma samples for the chroma block by applying theresidual block to the prediction information. At step 1711, the chromablock containing the reconstructed chroma samples is forwarded toward adisplay as part of a reconstructed video.

FIG. 18 is a schematic diagram of an example video coding device 1800.The video coding device 1800 is suitable for implementing the disclosedexamples/embodiments as described herein. The video coding device 1800comprises downstream ports 1820, upstream ports 1850, and/or transceiverunits (Tx/Rx) 1810, including transmitters and/or receivers forcommunicating data upstream and/or downstream over a network. The videocoding device 1800 also includes a processor 1830 including a logic unitand/or central processing unit (CPU) to process the data and a memory1832 for storing the data. The video coding device 1800 may alsocomprise optical-to-electrical (OE) components, electrical-to-optical(EO) components, and/or wireless communication components coupled to theupstream ports 1850 and/or downstream ports 1820 for communication ofdata via optical or wireless communication networks. The video codingdevice 1800 may also include input and/or output (I/O) devices 1860 forcommunicating data to and from a user. The I/O devices 1860 may includeoutput devices such as a display for displaying video data, speakers foroutputting audio data, etc. The I/O devices 1860 may also include inputdevices, such as a keyboard, mouse, trackball, etc., and/orcorresponding interfaces for interacting with such output devices.

The processor 1830 is implemented by hardware and software. Theprocessor 1830 may be implemented as one or more CPU chips, cores (e.g.,as a multi-core processor), field-programmable gate arrays (FPGAs),application specific integrated circuits (ASICs), and digital signalprocessors (DSPs). The processor 1830 is in communication with thedownstream ports 1820, Tx/Rx 1810, upstream ports 1850, and memory 1832.The processor 1830 comprises a coding module 1814. The coding module1814 implements the disclosed embodiments described above, such asmethods 100, 1600, and 1700 and/or mechanisms 1400 and/1500 as part ofintra-prediction 600, CCLM intra-prediction 700, mechanism 800, MDLMintra-prediction using CCIP_A mode 900 and CCIP_L mode 1000, and/or MMLMintra-prediction as depicted in graph 1100, as well as any othermethod/mechanism described herein. Further, the coding module 1814 mayimplement a codec system 200, an encoder 300, and/or a decoder 400. Forexample, the coding module 1814 can be employed to performcross-component intra-prediction to code chroma samples based ondown-sampled luma samples from the same CU and based on a comparison ofneighboring chroma reference samples and down-sampled neighboring lumareference samples. This may be accomplished according to equation 1 andequations 2-3 and/or according to equation 1 and equations 4-5.Specifically, the coding module 1814 down-samples the neighboring lumareference samples by employing a single row from a neighboring blockabove the chroma block and/or a single column from a neighboring blockto the left to the chroma block. As noted above, using a single rowand/or column reduces usage line buffer memory without significantlyreducing coding accuracy and/or coding efficiency. As such, codingmodule 1814 improves the functionality of the video coding device 1800as well as addresses problems that are specific to the video codingarts. Further, coding module 1814 effects a transformation of the videocoding device 1800 to a different state. Alternatively, the codingmodule 1814 can be implemented as instructions stored in the memory 1832and executed by the processor 1830 (e.g., as a computer program productstored on a non-transitory medium).

The memory 1832 comprises one or more memory types such as disks, tapedrives, solid-state drives, read only memory (ROM), random access memory(RAM), flash memory, ternary content-addressable memory (TCAM), staticrandom-access memory (SRAM), etc. The memory 1832 may be used as anover-flow data storage device, to store programs when such programs areselected for execution, and to store instructions and data that are readduring program execution.

FIG. 19 is a schematic diagram of an example system 1900 for employingdown-sampling while performing cross-component intra-prediction. Thesystem 1900 includes an encoder 1902 and a decoder 1910, which can beimplemented by a codec system 200, an encoder 300, and/or a decoder 400.

The encoder 1902 comprises an input module 1903 for receiving a videosignal partitioned into a chroma block and a first neighboring block.The encoder 1902 also comprises an encoding module 1905 for encodingprediction information for chroma samples of the chroma block into abitstream, the prediction information for the chroma samples determinedvia intra-prediction based on down-sampled neighboring luma samples, thedown-sampled neighboring luma samples generated from a single row ofluma samples from the first neighboring block. The encoder 1902 alsocomprises a transmitting module 1907 for transmitting a bitstreamincluding the prediction information for the chroma samples to supportdecoding and display of the chroma samples. The encoder 1902 is alsoconfigured to perform any of the steps of method 1600.

The decoder 1910 comprises a receiving module 1911 for receiving abitstream including prediction information for chroma samples of achroma block. The decoder 1910 also comprises a decoding module 1913 fordecoding the chroma samples for the chroma block based on the predictioninformation and down-sampled neighboring luma samples, the down-sampledneighboring luma samples generated from a single row of luma samplesfrom a first neighboring block. The decoder 1910 also comprises anoutput module 1915 for forwarding the chroma block toward a display aspart of a reconstructed video. The decoder 1910 is also configured toperform any of the steps of method 1700.

A first component is directly coupled to a second component when thereare no intervening components, except for a line, a trace, or anothermedium between the first component and the second component. The firstcomponent is indirectly coupled to the second component when there areintervening components other than a line, a trace, or another mediumbetween the first component and the second component. The term “coupled”and its variants include both directly coupled and indirectly coupled.The use of the term “about” means a range including ±10% of thesubsequent number unless otherwise stated.

While several embodiments have been provided in the present disclosure,it may be understood that the disclosed systems and methods might beembodied in many other specific forms without departing from the spiritor scope of the present disclosure. The present examples are to beconsidered as illustrative and not restrictive, and the intention is notto be limited to the details given herein. For example, the variouselements or components may be combined or integrated in another systemor certain features may be omitted, or not implemented.

In addition, techniques, systems, subsystems, and methods described andillustrated in the various embodiments as discrete or separate may becombined or integrated with other systems, components, techniques, ormethods without departing from the scope of the present disclosure.Other examples of changes, substitutions, and alterations areascertainable by one skilled in the art and may be made withoutdeparting from the spirit and scope disclosed herein.

What is claimed is:
 1. A method for cross-component prediction of ablock of video data, the method comprising: down-sampling areconstructed luma block to obtain a down-sampled luma block, thereconstructed luma block corresponding to a chroma block; determining amax luma value and a min luma value based on first down-sampled samplesof reconstructed top neighboring luma samples that are above thereconstructed luma block or second down-sampled samples of reconstructedleft neighboring luma samples that are left of the reconstructed lumablock, wherein the reconstructed top neighboring luma samples are withina single row being adjacent to the reconstructed luma block; determininga first chroma value and a second chroma value based on reconstructedneighboring chroma samples of the chroma block, wherein the first chromavalue and the second chroma value are respectively associated with themax luma value and the min luma value; deriving, parameters of a linearmodel (LM) based on the max luma value, the min luma value, the firstchroma value, and the second chroma value; and generating predictedchroma values of the chroma block based on the parameters of the LM andthe down-sampled luma block.
 2. The method of claim 1, wherein the maxluma value is determined based on values of one or more firstdown-sampled samples that are larger than values of remaining firstdown-sampled samples.
 3. The method of claim 1, wherein the min lumavalue is obtained based on values of one or more first down-sampledsamples that are smaller than values of remaining first down-sampledsamples.
 4. The method of claim 1, wherein the max luma value isdetermined based on values of one or more second down-sampled samplesthat are larger than values of remaining second down-sampled samples. 5.The method of claim 1, wherein the min luma value is obtained based onvalues of one or more first down-sampled samples that are smaller thanvalues of a rest of the first down-sampled samples.
 6. The method ofclaim 1, wherein the first chroma value is determined based on values ofone or more reconstructed neighboring chroma samples, wherein the one ormore reconstructed neighboring chroma samples corresponds to one or moreof the first down-sampled samples whose values are larger than values ofremaining first down-sampled samples, and the second chroma value isdetermined based on values of one or more reconstructed neighboringchroma samples, wherein the one or more reconstructed neighboring chromasamples correspond to one or more of the first down-sampled sampleswhose values are smaller than values of the remaining first down-sampledsamples.
 7. The method of claim 1, wherein the first chroma value isdetermined based on values of one or more reconstructed neighboringchroma samples, wherein the one or more reconstructed neighboring chromasamples corresponds to one or more of the second down-sampled sampleswhose values are larger than values of remaining second down-sampledsamples, and the second chroma value is determined based on values ofone or more reconstructed neighboring chroma samples, wherein the one ormore reconstructed neighboring chroma samples correspond to one or moreof the second down-sampled samples whose values are smaller than valuesof the remaining second down-sampled samples.
 8. The method of claim 1,wherein the determining a first chroma value and a second chroma valuebased on reconstructed neighboring chroma samples of the chroma block,comprises: determining, from the reconstructed neighboring chromasamples of the chroma block, a first chroma value and a second chromavalue respectively corresponding to the max luma value and the min lumavalue.
 9. The method of claim 1, wherein the first down-sampled samplesare obtained by down-sampling the reconstructed top neighboring lumasamples which are within the single row being adjacent to thereconstructed luma block.
 10. The method of claim 1, wherein the seconddown-sampled samples are obtained by down-sampling on the reconstructedleft neighboring luma samples.
 11. The method of claim 1, wherein thereconstructed left neighboring luma samples are within N columns whichare left of the reconstructed luma block, wherein 0<N<=3 and N is apositive integer.
 12. The method of claim 1, wherein the reconstructedleft neighboring luma samples are within a single column which is leftof the reconstructed luma block.
 13. The method of claim 1, wherein theLM comprises one or more of a cross-component linear model (CCLM) mode,a multi-directional linear model (MDLM) mode, and a multiple modellinear model (MMLM) mode.
 14. A method implemented by a decoder, themethod comprising: receiving, at a receiver of the decoder, a bitstreamincluding prediction information for chroma samples of a chroma block;decoding, by a processor of the decoder, the chroma samples of thechroma block based on the prediction information and based ondown-sampled neighboring luma samples, wherein the down-sampledneighboring luma samples are generated from a single row of luma samplesfrom a first neighboring luma block; and forwarding, by the processor,the chroma block toward a display as part of a reconstructed video. 15.The method of claim 14, wherein the bitstream includes data describingthe first neighboring luma block and a second neighboring luma block,wherein the first neighboring luma block is positioned above a lumablock corresponding to the chroma block and the second neighboring lumablock is positioned left of the luma block corresponding to the chromablock on a video frame, and wherein the down-sampled neighboring lumasamples are generated from a single column of luma samples from thesecond neighboring luma block.
 16. The method of claim 15, wherein thedecoding includes: down-sampling, by the processor, luma samples fromthe first neighboring luma block and luma samples from the secondneighboring luma block; applying, by the processor, a template to one ormore of the first neighboring luma block and the second neighboring lumablock to select the down-sampled neighboring luma samples; determining,by the processor, linear model coefficients based on the down-sampledneighboring luma samples; determining, by the processor, predictioninformation for the chroma block based on the linear model coefficients;determining, by a processor, a residual block for the chroma block fromthe bitstream; and decoding, by the processor, the chroma samples forthe chroma block by applying the residual block to the predictioninformation.
 17. The method of claim 14, wherein the predictioninformation for the chroma samples indicates the chroma samples arecoded according to cross-component linear model (CCLM) prediction modeintra-prediction, multi-directional linear model (MDLM) prediction modeintra-prediction, or multiple model linear model (MMLM) prediction modeintra-prediction.
 18. A method implemented by an encoder, the methodcomprising: receiving, at a processor of the encoder, a video signalpartitioned into a chroma block and a first neighboring luma block;encoding, by the processor, prediction information for chroma samples ofthe chroma block into a bitstream, wherein the prediction informationfor the chroma samples is determined via intra-prediction based ondown-sampled neighboring luma samples, and wherein the down-sampledneighboring luma samples are generated from a single row of luma samplesfrom the first neighboring luma block; and storing, in a memory of theencoder, the bitstream including the prediction information for thechroma samples to support decoding and display of the chroma samples.19. The method of claim 18, wherein the video signal is furtherpartitioned into a second neighboring luma block, wherein the firstneighboring luma block is positioned above a luma block corresponding tothe chroma block and the second neighboring luma block is positionedleft of the luma block corresponding to chroma block on a video frame,and wherein the down-sampled neighboring luma samples are generated froma single column of luma samples from the second neighboring luma block.20. The method of claim 19, wherein the encoding includes:down-sampling, by the processor, luma samples from the first neighboringluma block and luma samples from the second neighboring luma block;applying, by the processor, a template to one or more of the firstneighboring luma block and the second neighboring luma block to selectthe down-sampled neighboring luma samples; determining, by theprocessor, linear model coefficients based on the down-sampledneighboring luma samples; determining, by the processor, predictioninformation for the chroma block based on the linear model coefficients;determining, by a processor, a residual block for the chroma block basedon a difference between the prediction information and the chromasamples; and encoding, by the processor, an indication of anintra-prediction mode and the residual block in the bitstream torepresent the chroma samples.
 21. The method of claim 18, wherein theintra-prediction employed to encode the chroma samples includescross-component linear model (CCLM) prediction mode intra-prediction,multi-directional linear model (MDLM) prediction mode intra-prediction,or multiple model linear model (MMLM) prediction mode intra-prediction.22. A method for cross-component prediction of a block of video data,the method comprising: down-sampling a reconstructed luma block toobtain a down-sampled luma block, the reconstructed luma blockcorresponding to a chroma block; obtaining first down-sampled samples ofreconstructed top neighboring luma samples that are above thereconstructed luma block or second down-sampled samples of reconstructedleft neighboring luma samples that are left of the reconstructed lumablock, wherein the reconstructed top neighboring luma samples are withina single row being adjacent to the reconstructed luma block; derivingparameters of a linear model (LM) based on: the first or seconddown-sampled samples, and reconstructed neighboring chroma samples thatare above the chroma block or reconstructed neighboring chroma samplesthat are left of the chroma block; and generating predicted chromavalues of the chroma block based on the parameters of the LM and thedown-sampled luma block.